HELP PLEASE!! ATI X850 XT PE serious problem, inexplicable system hangs

My computer was on and idle, only windows desktop was displayed, I was away from room, when i came back found system turned off, turned on again, and tried loading a game (counterstrike source) game loads fine, once actual gameplay begins (3d engine is loaded etc.) game hangs, system restarts, control center also hangs whenever 3d preview is displayed under 3d section, tried other games (warhammer 40000), also hangs once actual levels are loaded, system either restarts or displays black screen with white lines then restarts with long beep, sometimes system does not start and just emits a longer beep than usual. I have formatted my drive and reinstalled entire operating system, also tried 5.4 catalyst drivers, which is the last version i know worked perfectly, i am unable to run any 3d applications now, i have also removed and reinstalled my graphic card (it looks fine), and also reinstalled my bios file and rechecked all its settings, just in case prob originates from there, temp. levels seem ok too (around 50 celsius at idle) too, i have barely had this product for six months, and i am unable to run anything which involves 3d rendering it seems, does this mean my card is damaged or ruined?

 

try diff memory

 

u prob have already checked, but may of overlooked is your div x up to date.

 

divx etc. is updated, my ram has been working fine for months, why would it stop now? my specs:

Asus A8n sli Pci Express mobo
athlon64 3500+
Ati radeon x850xt PE 256mb
1gig corsair xml ram
10,000rpm raptor sata hdd (primary)
7,000rpm seagate barracuda hdd
win xp professional sp2

 

check that your RAM, Graphics card, ans hard drives are properly plugged in (unplug them and put them back in) and that the power supply is plugging into them snugly. It very well could be that your PSU is going--its becoming increasingly important to have a GOOD power supply these days, especially running a higher end system like yours.

is there another PCI-E video card you could try using for a little to verify that its not your card thats simply bad?

 

I think I found the solution, i changed position of CMOS jumper from mobo to erase bios and reset at default settings since reflashing it by cd or floppy seemed to keep my old settings and card seems to be working now, it still worries me that I have no idea what has caused this problem since it just seems to have happened randomly, thank you all for your help though. btw, i have a brand spanking new enermax 450W atx 2.0 compliant psu, dont think that was the prob.