System freezing

[stanneruk]

Not sure if this is the right place to post but....
i built a cheap pc from scratch with a friend of mine, and works 90% of the time, but my entire system freezes when running games and it seems completley random.
when i first built it i had the nvidia geforce 9800gt the screen would go black, the sound would stutter then stop and i would have to restart
i ended up with a 9800gtx (not so different lol) so i swapped them over, now the same thing happens but slightley different,
eg.
dawn of war II retribution: grey screen, sound stutteres
Battlefield 3: black screen and sound stutters
titan quest: yellow\cream screen and sound stutters
and other games. also happens while watching videos.
yet sometimes can play for hours on end with no problems
any information would be helpfull


MOBO:Asrock M3A770DE 770 Socket AM3 8 Channel Audio ATX Motherboard
Processor:AMD Athlon II X2 250 3.00GHz
PSU:CIT 700W Black Edition PSU 12cm Fan Dual 12v Rail 20+4pin 2x SATA
GPU:NVIDIA GeForce 9800 GTX (285.62 drivers)
O\S:Windows 7 Ultimate N 64-bit

 

[clutchc]

You don't mention how much memory you have installed on the board. But try cleaning your system with CCleaner. Do the Clean and Registry both. Then uninstall the graphics driver, boot into Safe Mode, run Driver Sweeper to clean out remnants of any old Nvidia/AMD video drivers, and re-boot into Windows. Re-install the new driver. Defrag.
CCleaner: http://www.piriform.com/ccleaner
Driver Sweeper: http://phyxion.net/item/driver-sweeper.html