you are running this System on 262W?????
unbelieveable!!! for graphuc cads requiring external Power, one's PSU should at least be 350W for optimal performance, as upgrading BIOS wont cost u anything, try doing it first, if it hepls, still I wil strongly recommend PSU Upgrade in every case if you are running this system.
normally you wont experience such problems while watching Movies, Playing Music or general work, whike 3D or even 2D games are running, GPU is at boost, so it requires optimal flow of current across.
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"