So my friend wanted a gaming PC and I thought I might as well give it a go building him one since I've always wanted to do it. I'm so disappointed in myself, after the thought I put in to it I didn't think it'd be too hard but I've fucked up somewhere. Basically, here's my problem. 
 

Parts:

I'm not sure exactly what your saying, however do you have a manual for the mobo? If you have a manual for the case and also the mobo, it should tell you where to put all the wires and where to put the wires. Or you can youtube the mobo and see how other ppl puts it together because you could of made a mistake.  
    
Do you even have a bios screen? I know it's not much help for now, however can you at least tell me what is the mobo?

" So my friend wanted a gaming PC and I thought I might as well give it a go building him one since I've always wanted to do it. I'm so disappointed in myself, after the thought I put in to it I didn't think it'd be too hard but I've fucked up somewhere. Basically, here's my problem. 
 

Parts:

Case - Antec 900
CPU - i5 760
RAM - 4GB DDR3
GPU - GTX460 1GB
PSU - 650w Modular (I can't remember the exact one, he
 

1. Turning it on I can see the LED on the motherboard to indicate that it's receiving power. The CPU cooler starts up just fine. Nothing going to the monitor at all. I don't have any idea what is and isn't working because it doesn't boot at all or indicate that the motherboard is working despite it looking like it's on. The hard drive is completely empty so I need to install the OS.
2. The PSU is modular, and I attached the main 24 pin connector to the motherboard and there is a second 8pin one built on but I can't find anywhere on the motherboard to put it. Do I even need to use it?
3. I don't know how I should be supplying power to each component (e.g. which cables to use). I've got 2 6 pin on the GTX460 going to 8pins in to the PSU and I have absolutely no idea if that's right. Maybe you can't even tell me, but I need help for where to look.
4. I don't know how to supply power to the fans. The connectors are standard not special fan ones for the motherboard, and I don't know what type of connection it is.
   

 I feel like I've let him down, and I'm so annoyed at myself. I wanted it to go smoother than this. I would really appreciate the communities help. "

Make sure the power supply supports modern video cards.

Modern Video cards need direct power from the power supply not just from the PCI-Express slot on the motherboard.  It should be a six pin connector and will plug in to the video card on the end inside the case.  Sometimes they have a six pin and a two pin stuck together, because some devices require eight.  In that case, two of those pins should slip off and away from the other six if that is all you need for your video card.  Examine the connector from the power supply carefully, it should be easily recognizable that two pins can be separated from the other six.

There's a four pin connector to power the CPU, 24 PIN to power the motherboard.  You may have only supplied power to the CPU fan and not the CPU itself.

On the motherboard/case, match up all the pin numbers (ie., pin 1 case wires matches pin 1 on motherboard, ground to ground etc., for the correct device  such  as power on/off, USB, Fans, etc.).

This should all be in your motherboard, case, power supply, video card, etc manuals.

It wouldn't hurt you to find a recent guide for building your PC and read the whole thing carefully, then start from scratch.

New builders can take 10 hours or more before they get it right, so don't be discouraged, but you will have to read, study, and ask questions to learn the ropes.  Experienced builders can usually have it up and running ready for an OS install / stress test in less than an hour.

P.S. Never skimp on a power supply.  A 650 Watt continuous is preferred over modular. More than one rail was preferred in the past, but not so any longer.  A single rail continuous with high efficiency is an overall better power supply.  BTW, what brand name is your power supply?  What efficiency rating?  How many rails? You may be better off sending it in for a quality brand replacement.

 The PSU is modular, and I attached the main 24 pin connector to the motherboard and there is a second 8pin one built on but I can't find anywhere on the motherboard to put it. Do I even need to use it?  

Most of the time when I am working in my pc and I bump the video card (GTX 280) power connector, the video card will emit a continuous beep upon boot. A GTX 460 may exhibit similar behavior. 
 
Speaking of beeps, is the onboard speaker plugged in? If so, are you hearing any beep codes upon boot? The PC will emit a solid beep if all is well, and a beep sequence if it encounters problems. If there are no beeps at all, you may just have a dead mobo/CPU.
 
Edit: Have you tried doing some simple stuff to troubleshoot this (reseating CPU, all expansion cards, cables etc..)?

@PDC_Emulator: No sound from the motherboard, so I'm guessing not. Reading the manual I saw that I needed to connect one of 2 audio cables from the case and I think I connected HD audio right but that probbably has to do with the sound ports on the front of the case and not the beep from the motherboard, right? "

1. your atx 12v 4pin seams to be unplugged for your posts, looking at the case there seams to be hole to put the 4pin connector near the psu but I can't see if it comes out at the top if you can't find out how to do it that way there are extenders for it  
2. the 8 pin is for certain video cards, looking a a few gtx460 they use dual 6pins 
3. things that need to be plugged into the psu are video card and hdds, there are 2 types of hdd connections the fat 4pin are molex and are used with the wide ribbon cable, the other are for sata (they probably have a name but I've never herd it =P)
4. sounds like your fans are using a jumper style plug which are on your mobo the manual has the location of these seams to be page 1-7 figure 1.5.3 there is one for the cpu fan and 1beside for a power fan (can be used for case fans) and one in the centre of board for case fans they are all labelled like the figure 
 
also seeing it is an asus board it probably has a white connector block for all the power buttons leds etc which should be quite easy to use (I love these =D)

Are you sure you can't snap the 8 pin in 4? Take a picture of your mobo with your current connectors and take a picture of this 8 pin connector cable. I myself use an antec 900 myself so I have the manual and the case, so i'm familiar with it if I remember where I plugged everything.

Also I couldn't edit this in for my last post, can you figure out what psu are you using? Is it a cosair modular psu? Maybe I can see the actual connectors and stuff because the 8 pin should be able to use a 4 pin. Maybe you have to snap it in two and you didn't realise you could.

" @gilsham:  what is overheating? "

@AlisterCat 
It should start up and then tell you that there is no bootable device (or something to that effect). This does sound like a CPU thing, you should check if the heatsink and fan is properly secured and that there's a good layer of moist thermal paste on the heatsink pad.

While we're on the subject, I need some help too. My computer works fine, but my 5750 does not seem to. I've put it on, and there are two 4-pin power cables. What do I do with them? Nothing is connected to the 5750 at the moment-the only thing I've done is put it in the PCI Express.

" I have three hardrives, the first is an SSD, second is a WD black sata 3 6gig per second (as falsely advertised)
"

" @AlisterCat:  Did you manage to get a keyboard working/connected to the PC you're building? I thought that you said you couldn't manage this so far. Is it a wired or wireless keyboard? If it's wireless try a wired 1, it might just be that the keyboard hasn't managed to get synced with the reciever."

 @AlisterCat:  That seems to suggest that the USB Ports are not working or they are incorrectly configured, I'm assuming that you are connecting the keyboard to the backplate of the mobo and not using the ports at the front of the case, if so unplug the case's USB connectors from the mobo just in case they are causing interference.

I've had a look at the manual, this mobo uses jumpers to configure wake up on USB the default setting is to have pins 2 and 3 connected, try moving the jumper to connect pins 1 and 2 for ports 1-8 which should give you +5v to the back panel USB Ports.

As you have had some messages come up on the screen I think it is safe to assume that your RAM is ok, though just in case remove all but 1 stick and ensure that the stick you leave is in slot 1. Disconnect the power connectors to all of your hard drives and optical drives until you can get it to post and get into the BIOS settings.
 
@HitmanAgent47: I'll give that a go and PM you my results, so as not to derail this thread (I somehow end up doing that! Sorry).

It was the only thing I could think of, looking through the manual, clearly you will not be able to move forward without resolving the keyboard issue. Hopefully someone else with have an answer, there's nothing on it on the ASUS forums. Maybe you should try contacting the guys that sold the mobo and see if they can offer any technical assistance.

I have updated the first post since you guys were so great and helped me with that. It would be so much easier if I had it here because then I could at least try stuff. Oh well. Still need thoughts on whether it is over heating, and why it might be overheating etc.

Your motherboard may have some misplaced solder somewhere on the traces. Have you given it a good once over to see if anything is there that could be causing it to short/overheat?

I've been speaking to a friend and he said it might be a RAM issue. Gah... so many things that could of gone wrong.