I have only got Minecraft recently and have tried to mod my game (horrid mistake No.1) 
 
This process failed miserably and when I tried to regain my file, I must have backed up my bin or jar badly... 
the game is corrupt, everytime I try to play browser or not, it goes black and not responding 
 
I have tried to  delete and redownload to the game again but to no avail :/ 
I am expecting some shit from you dudes for modding it but I'll raise my hands as to having done this to myself, just trying to salvage it... so guys am I basically forever fucked now? :S

I've modded with almost no problems (though just with rather simple ones). Try and delete the Minecraft Bin folder as a whole. When you restart Minecraft it should re-download it. The one thing I don't like about modding is that you can play MP with it. Eh, guess it's good to keep two versions of the Minecraft Jar file.

Anyway, that's all I can really say to try and help. Each time it went to black for me, I deleted the entire file and had it re-download. Worked fine.

Maybe it would work if you not only delete the bin, but the whole file.
 
Which is:
For Windows 7 and Vista
C:\Users\<YourUserName>\AppData\Roaming\.minecraft
 
Windows XP  :
 C:\Documents and Settings\<YourUserName>\Application Data\ .minecraft 
 
If you already tried this I don't know what to tell you. But re-purchasing the game won't help because that's just changing the account from free to premium. Which has nothing to do with the files on the computer.
You could always ask the folks down at the Minecraft Fourms.
 http://minecraftforum.net/index.php
Good luck.