PC is giving trouble to start and is BSOD'ing

Ok my old rig which i am lending to my sister is giving her problems,and i am not sure what is wrong.

For some reason sometimes it takes a few tries to get it to boot at all,and when it does work, it will end up blu screening.

The weird thing is it was working,just fine,until my brother in law went to install an old ide hd(to set up for him to use in my ps2),and when he opened the case to install the drive he noticed the 24 pin was lose,and he pushed it in.

The specs are:

Intel [email protected]

XFX 680i LT

2x2GB Patriot Viper 1066mhz

EVGA GTX460 SE 1GB

Ultra X-Pro 600w

320GB WD IDE hard drive

and the drive that was put into the system to be formatted for my ps2 was a seagate 60GB IDE.

What do you guys think is wrong?

Ok i fixed the BSOD,wen put in another video card as a place holder while clean up the old one,cause it was so caked in dust that i had to hake off the heatsink just to clean it enough.

But i have never taken off a gpu heatsink before,and the chip is at least 1&1/2 times the size of my cpu lol.

How much thermal paste should i use on it? 

Ok NVM it JUST BSOD'ed agian,but this time it was different the last time,and it said something about "Phisical Memory Dump",oh i also forgot she is running windows 7.

get high res pictures of the blue screen the bottom half is the most important.

I would reinstall os, and check Hard-drive settings in BIOs. Best of luck

Well i finally got look at it myself and i think i know what caused and i think i fixed it,the GPU and CPU cooler were caked with dust the cooler was so bad i was able to peel the dust off lol,but i will post back if it blue screens agian.