Random Freezing in Windows XP

[Mark W]

I am running Windows XP Pro. Over the last month, my
computer has begun a pattern of random freezing. This
started when the computer screen saver would activate.
After clicking to remove the computer out of screen saver
mode, the mouse and screen updates, e.g. start menu would
get very sluggish and become unusable. I found that
doing a hard reset or powering my computer off is the
only way to get around it.

One month ago, I decided to completely reinstall Windows
XP. Since that time, I have encountered freezing
intermittently. There doesn't seem to be a specific
cause, e.g. software or hardware. I have rebuilt my PC 5
times in one month and I continue to experience this
issue.

I have scanned for viruses, applied the latest Windows
patches, download all Windows updates on a regular basis
and tested my system memory. At this point, I don't know
what else I can do to correct this problem.

Any information that might pinpoint the cause of this
problem would be greatly appreciated.

Thanks,

Mark