I am running on a athlon 1.4, 512mb ram, geforce 2 GTS, creative sb live, 2 HD, 1 cd rom, 1 floppy drive, 1 network card, 2 extra casing fan, P/S2 keyboard, 1 usb mouse, 1 usb webcam, 1 usb pad. All drivers are updated to the latest provide by the respective maunfactorers, except i never update any of the motherboard bios, just the graphics, network and sound card drivers.

With the above system i am running in a 350 watts power supply, when my brother was playing game, the whole system went blank, and he ask me to see whats the problem i check the power, trying to on the comp but no respond so i guess is the power supply problem.

So I get a new one 400 watts, so i installed it, everything was running smoothly until he play game again( note: i test it by playing a game as well but nothing happen) then the whole thing shutdown again, and again no power when i try to power it up. So i guess is the power supply newly purchased is dead.

So i assume is the power supply fault so i go and exchange for a new one, the shopkeeper test the power supply and determint that the power supply 400watts i just bought from him is dead, so he exchange one for me, but after series of testing which one is working, finally he found one that is working, but I and him don't know its a 300 watts power supply. So during my way home i take a look at it and found out its a 300 watts, so i am thinking anyway let me try it to see if the power supply will go dead again when i install it. So after installing it until now where i am typing this help message the system is running ok. BUT sometimes when i start up the computer it will freeze at the desktop when loading other programs which is not that often, but once i am at the desktop with everything up it will not freeze at all, so i can do all my stuff like checking emails and surfing net. But once i try to play games, it will 100% freeze for sure just a matter of time. The longest time i can run a game is for about 30 mins, and the games are in 3D, i can play other games like chess which is in 2d mode with no problem not full screen as it don't allow full screen, but i don't think full screen or window screen is the problem. I want to change the 300watts back to 400watts but the shopkeeper say he don't have any more stocks yet, so here i am trying to find out if it is really the power supply problem.

Another info is i got a cpu monitor program which tell me about temperature lvl and voltage.
The temperature range from 52 to 62.
Voltage for core is 1.79V-1.80V
+3.3V is 3.41V
+5V is 4.50V but when i run game the voltage will drop to 4.42 the most(the game is 3D game, don't seem to have any effect when running 2D)
+12V is 12.48V

Your machine will probably run on a 300-watt power supply without too many problems. However, you do have quite a few USB devices that might require a higher wattage power supply. I would try to get at least a 350 but would feel ok with the 300 watt as a backup.

I would try swapping out the video card for a new one or one you borrow from a friend. See if this has an effect when you run your games. If your power supply is ok, then you should probably buy another video card. It is entirely possible that the video card was causing a short.

Of course, if your power supply still fails, you may look at removing hardware and USB devices from the computer to see if one of them is causing the short.

If none of this works, it is time for a new motherboard.

Hope this helps.