Computer Completely Shuts Itself Down

[Magicb6076]

All,

Have been having a major problem with my desktop listed below...the Gateway 820GM. At random moments, whether I am watching a video or browsing the internet, the computer completely shuts down. I don't mean I see the log off screen and then it shuts down, I mean a slight freeze in the screen, and then an instant black screen because of no input to the monitors. What's interesting is that my power light is still on the case of the computer, and it still sounds as if the fans are still running, just nothing on the screen. This past weekend, I didn't have any problems with it. I was rendering some graphics in 3D Studio Max, some taking 30 minutes, and didn't give me any problems even with my CPU at nearly 100%. It seems that simple processes such as the ones listed above are doing it. I even ran several malware, spyware, and virus tests last night to see if anything fishy was going on. Even with the strain on my computer of those programs running, it remained on. Does this suggest a possible hardware issue or something with software? Any Clues would be helpful. Thanks!

[not important]

My first guess is the Power Supply.

[Magicb6076]

Any reason why the power supply would fail at browsing the internet or watching video moments and not during intense rendering in 3D software programs?

[glc]

The power supply was suggested because name brand computers generally do not use power supplies with any extra margin. However, this may be a simple overheating issue. Open the computer and blow out all the dust, paying particular attention to the CPU and video card heatsinks, and make sure all fans are running properly and are clean.