Freezing/Black Screen Desktop Problem

My brother's computer has been semi-functional for over a year now. Here's the problem in specifics. The computer will start up, it never has a problem doing this. Desktop comes up, programs load. While running there is no notable slowness, everything functions as it should. At any random interval, and usually it's within the first ten minutes, the image freezes (including an immobile mouse) and the sound will stutter. This lasts for about a second, then, the screen goes black. The computer itself does not power down. You press restart and repeat the process.

It can happen within a few seconds, a half hour, a whole day. There is no apparent cause. The tower does not have to be physically disturbed and no programs have to be open. You can do nothing but press reset and be greeted by a black screen five minutes later without touching anything.

Other times it will run for days, seemingly indefinitely. Sometimes you get lucky and it just stays on. Except it never lasts as Windows automatically searches for updates and then eventually automatically gives you a restart timer. Seeing as nobody can man the computer 24/7, it will be restarted at some point by Windows updates and then it will freeze again.

We've tried different monitors and vga cables. In research of the problem, my brother has found that everything he googles about the issue tells him that his power supply might be bad. Just recently, there's been a brand new one installed. The result's been the exact same thing.

Now here's the really strange part. Our dad is the computer guy in our family. He built both mine and my brother's computers and mine has worked without a problem for seven years. He's pretty knowledgeable. So we hand the thing over for him to observe the problem and tell us what he thinks. Except it doesn't happen. He had the computer in his possession for weeks and it never froze on him. After a little while we asked him to restart it as it could just be one of those fluke lucky runs. So he does just that on a daily basis for awhile. In spite of this, it never froze in his possession once. We take it home and it freezes for us almost immediately.

So most importantly, what could be causing this other than what's already been ruled out. And as an aside, what in the world could be the explanation behind the machine having no problems at a different location?

Jam it back in, in the dark.

Problem is, and I don't know if you could tell this by the previous post, but me and my brother are roommates and my computer does not have the same problem. Additionally we've moved into a new place just this weekend. Does the same thing with just about none of our other appliances even set up.

There's nowhere I can't reach.