this is a new problem for my pc !! games used to work very good but then this problem started to happen my pc has intel core 2 quad and a 1 gb ddr5 sapphire 6770 and gigabyte p45 motherboard and 350w hec power supply i think the problem is because the power supply because after 3 years it may be having lower efficiency or maybe the vga card it a new 1 got it from feb 2012 but it was working very good !! till this started to happen !
I would upgrade the power supply to a good one. A 500 watt would be plenty with room to spare, Corsair, Seasonic, Antec are good brands. If you want to do some research on power supplies go to ( hardwaresecretes.com) and click on power.
For a system using a single Radeon HD 6770 graphics card AMD specifies a minimum of a 450 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 23 Amps or greater and have at least one 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated @ 45°C-50°C ambient temperature, is the most critical factor.
HEC 350W power supplies usually have a combined +12 Volt maximum continuous current rating of 23 Amps. HEC power supplies are not tolerant of being stressed near their limit especially the lower end series.