Monitor Blacks out

hey guys i tried searching all over the internet for a solution to this problem, none of the actually helped, so heres my situation.
begining of this summer i bought and built my own computer,

its a XION Solaris black case
nForce 650i Ultra ATX Intel Motherboard
GeForce 8800GTS 640MB
Intel Core 2 Duo 2.4GHz Processor
2gb ram
400 gb hardrive space
and a TruePower Trio 650 Watt ATX 12V Power Supply
the screen is a X2gen 22 inch wide screen

using windows xp media center

anyways, when i got it during the summer everything worked fine, i was playing most games on highest quality, overlord, oblivion, bfme 2. during the second week the harddrive broke, so i returned it and got a new one and reinstalled windows xp media center.
later that week i instaleld wow and played it, it worked fine for the first couple of days then i started noticing the computer montior screen blacking out, with no specific pattern, i could be loading or going through a portal or on a zepplin the monitor would jus black out, the sound still works for a few seconds but often it gets glitched and repeat it self. and wen the monitor blacked out i would have to wait a few hours, sometimes repluging all the cords, and if that didnt work i had to open up the computer and make sure the hardware inside was plugged in rite, and it was. nex i start up the computer again and hope for the best. but most of the times, it would either die at the windows logo screen, or the login screen, and if it didnt black out there when i open a picture, web browser, or even send a msn or aim message my screen would go black. the graphics card feels pretty hot sometime sbut my friends tell me its supose to happen, and i feel my power supply and its also hot and my friends say thats also supose to happen. so currently im at a complete lose here, im using my computer every day with the fear of black screen when i play a game or watch a movie, if a black screen occurs then the computers practically unusable for the nex couple of hours or even days as everytime i turn it on a few minutes the screen would die again. i have figured that high quality graphics games like bioshock or World in Conflict when a nuke goes off my screen blacks out. the current driver version im using is 162.18, before i used 15xx something and that problem also occured. 3 of my friends have almost the same exact build as my current computer and they are not experiencing any problems.

it would be appreciated if anyone can help me with my issue. thanks alot.