Computer hardware problem (long question)?

here is my spec and problem. its fairly long but i have to explain

specs:
asus p5q pro motherboard
intel q6600 cpu
antec true power trio 650 psu
old crappy ati card // new ati 4870 graphics card
old ide harddrive // new sata harddrive
ocz reaper ram 2x2gb

two weeks ago my pc turned off immediately when playing games or sometime other intensive things. it happened about 4 times then wouldn't come on. So i took the mobo and graphics card (old crapy card) to the local computer shop and they said the mobo was fine but the graphics card was faulty. i braught the stuff home and rebuilt my computer and it worked!?! but still turned off when playing games which i was not bothered about because i was getting a 4870...

when i got my 4870 i was playing a game that was on the old ide hard drive and it turned off. (anger increasing)
so i installed a fresh windows onto the new sata hdd and installed a game which played without shutting down.
then i started transferring files from the old ide hard drive to the new sata hard drive and running a colour calibration test for the screen and it shut down. (good high level of anger)

it is now behaving like it did before i took it to the shop with the old graphics card. all the fans and lights start like normal but there is nothing happening on the screen (orange standby light)

is it static in the psu?
is it the old ide hard drive overheating?
is the motherboard broken (pc shop tested it and said it was fine + worked for me after 1st crash)
is the psw broken (worked after mobo came back from shop)

helppppp