Im a guy with not much knowledge about hardware and stuff. Recently I have decided to upgrade my video card. So I bought an Gigabyte HD4870 1gb yesterday to replace my 9600GT.
It runs well for a while until I do the Vista Performance Rating Test in the Games sections to update my Rating, the PC suddenly turns off. Monitor goes off, power light on the PC goes off but light on keyboard still on. I try to turn the PC on but it wont turn on. I have to unplug the power cable or turn off/on the power supply and wait for a while, then turn on the PC again, now it is on.
When I play Crysis Warhead and put it to higher resolution than usual, the PC turns off again.
Thought the card was faulty, I exchanged the card for a Gigabyte GTX260 today and it still has the same problem.
It sounds like a power problem to me. When the PC is getting under a heavy load (drawing more power from the power supply) it can't put out enough power and shuts down. The other side of that could be an overheating problem. I'm not really sure what you have for a motherboard, but you're going to need to check the temperatures and see if something is overheating. What brand of PSU do you have?
Yeah unfortunately it sounds like you are one of the many victims falling prey to the bad power supply manufacturers. You'll find all the experienced builders are going to always recommend getting a good power supply from the best manufacturers, rather than trying to skimp one it. This is pretty much exactly why. Good news for you is after a mail in rebate you can get a power supply good enough for your system for $40.00. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
I checked again and it appears that before the PC goes off, it says "to Power Saving Mode".
Sorry I forgot to mention my motherboard: Gigabyte MA78GM-USH2, its kind of a mini motherboard with only 1 PCI-Express slot.
My PSU is SHAW which has bad reputation they say.
shaw.....oh dare god. Some of the worst power supplies I have seen in a long time. When your dealing with power supplies it is always best not to cut corners. Always buy from a very well known name brand that uses the best in their builds. OCZ, Antec, and mostly likely at the very top is Corsair though there are many others.
That OCZ Fallen linked to will do great and is even modular which is a very nice touch for such a affordable PSU. If you ave the money though I would suggest one of their 600w PSU's though.