Windows XP Media Edition Problem

A very odd problem has been repeatedly occuring on my Windows XP Media Edition PC.

It seems like when my computer is "busy" either opening up a new program, loading a web page, or using Media Center my computer screen turns black for about a half a second then returns to whatever I was looking at.

The screen is black, does not say anything. It is the same screen that pops up when the computer goes to "sleep" so I don't think its a virus. I think it may be a problem with memory, seeing that it only occurs when something is loading, or a program is running that takes up a significant portion of memory.

Any suggestions? I regularly run your recomended virus scans and my computer is clean.

I don't know what is causing my screen to go to black, but would really appreciate any help.

Thanks