I made a post last week describing my current rig and what I could do to get ready for Elder Scrolls V: Skyrim.  I refuse to play it on a 360.  I'm not a PC purist but I do believe some games are better on certain system.  Never going to play a 3rd person shooter on a PC, etc.  So, I bought a new CPU cooler and got the temp. down to around 40C with no load and 45C with full load using Prime95.  I got my E6300 @ 1.8Ghz up to about 2.6Ghz stable with a temp. of 55-58C at full load and put the OC on the memory at 2.50 so it came in close to 1000 MHZ.  I also replaced my over voltage 2 gig RAM with 4gigs of RAM. I also, today, installed a EVGA GTX 550 Ti 1gig (Fermi).
 
Now, its still weird.  Every time I try to benchmark with 3dMark Vantage it locks up. (Note: it did this before with a GT 9500 1gig).  It will either freeze the system and hitting the ESC key just gives me a black screen.  I can run Fallout: New Vegas on Ultra settings and it runs pretty smooth but I keep what appears to be frame skipping every so often.  I can't narrow down whats going on.  I thought maybe I was having some really bad ghosting on my monitor but I can't recreate it on the desktop by moving windows around. Something as simple as closing Steam is slow.  Things my computer should annialhate with my specs can be choppy, even Facebook games.  I get mini-freezes that are annoying to the extreme.   
 
So, anyone have any guesses?  A poor power supply?  Motherboard finally giving out?  Processor still to slow?  Harddrive issues? 
 
TL:DR: Shits messed up and Winter is coming! (Skyrim)

@Zombieheadbutt: Most problems i've had with system lock ups have been from bad RAM. Try putting in one stick at a time and test each stick individually. Outside of that i have nothin else for ya.

First check that 3dMark Vantage runs with everything at stock, then OC half way and try again, then keep upping your overclock in small stages until  you can't run it without crashing, when it crashes you can dial it back to the previous settings. Plus you can  run a program like HWMonitorso you see the voltage requirements as well as the temps, it might just be that you require more voltage through CPU, RAM or other components.

re-install window. if your problem is still there afterwards it has to be a hardware problem. in which case you can isolate from there. but until you know if its either a software or hardware problem its pointless trying to guess.
 
oh and by the way 3rd person shooters are great on the PC with a 360 controller. its just like playing them on the 360 but with great graphics. 

@jetsetwillie said:

oh and by the way 3rd person shooters are great on the PC with a 360 controller. its just like playing them on the 360 but with great graphics.

Seconded!

Set your ram to stock clocks and try running P95 for 6-8 hours, if it doesn't have any issues running that long then you can eliminate your CPU clock as being unstable. I wouldn't suggest overclocking ram at all unless you really, really know what you are doing... The performance you get out of OCing ram is not enough to be worth the hassles that come with it.

A general rule of OCing is to OC one component at a time then stress test to confirm stability, that way you know what component is stable/unstable.

how long did you actually stress test your system? As other people said I recommend testing stuff in small increment and for the last OC stress test for 12-24hrs. Locking up is most likely the problem with your OC, the benchmark programs push the system way more than game would

@Zombieheadbutt said:

I made a post last week describing my current rig and what I could do to get ready for Elder Scrolls V: Skyrim. I refuse to play it on a 360. I'm not a PC purist but I do believe some games are better on certain system. Never going to play a 3rd person shooter on a PC, etc. So, I bought a new CPU cooler and got the temp. down to around 40C with no load and 45C with full load using Prime95. I got my E6300 @ 1.8Ghz up to about 2.6Ghz stable with a temp. of 55-58C at full load and put the OC on the memory at 2.50 so it came in close to 1000 MHZ. I also replaced my over voltage 2 gig RAM with 4gigs of RAM. I also, today, installed a EVGA GTX 550 Ti 1gig (Fermi). Now, its still weird. Every time I try to benchmark with 3dMark Vantage it locks up. (Note: it did this before with a GT 9500 1gig). It will either freeze the system and hitting the ESC key just gives me a black screen. I can run Fallout: New Vegas on Ultra settings and it runs pretty smooth but I keep what appears to be frame skipping every so often. I can't narrow down whats going on. I thought maybe I was having some really bad ghosting on my monitor but I can't recreate it on the desktop by moving windows around. Something as simple as closing Steam is slow. Things my computer should annialhate with my specs can be choppy, even Facebook games. I get mini-freezes that are annoying to the extreme. So, anyone have any guesses? A poor power supply? Motherboard finally giving out? Processor still to slow? Harddrive issues? TL:DR: Shits messed up and Winter is coming! (Skyrim)

Why are you overclocking the memory too? Run it in a 1:1 ratio with the FSB, anything higher with a 775 system is useless as it's still limited by the FSB.

Frame skipping is common with the Fallout games, it's something to do with the engine. Unfortunately, there isn't much you can do about it, but there are ways to alleviate it (F:NV 4GB).

As others have said, run P95 for at least 6 hours to make sure your overclock is actually stable. And as another person mentioned, try pinpointing the issue by dealing with one thing at a time. For example, make sure the motherboard can handle the FSB frequency you're at by lowering the CPU multiplier and making sure the memory isn't overclocked. Once that's confirmed to be stable, raise the multiplier back again and test the CPU. Raise voltages as required (don't go over 1.5v for the CPU, 1.45 for FSB Termination, and 1.5v for the MCH/Northbridge). And again, don't overclock the memory, it's fairly useless for a 775 system and usually just nothing but trouble.

Good luck!