Freeze, blink, repeat

I thank you in advance for any assistance with my issues. Please let me state that I really do not have the vocabulary to properly describe my issues, but let me get to the point.

Recently, my system will freeze, go black(for no more than a couple of seconds), then will re-appear with the remnants of the previous view and a refreshed one. This is more prominant especially when I go to a fresh site or navigate within one.

I have checked NVIDIA for any video driver updates and have reinstalled the ones I have. Multiple virus and Malware scans have been fruitless.

SpyBot
ASquared
Avast
CCleaner
HiJackthis
Spyware Blaster
etc...

My system, although rather ancient, has run flawlessly until recently:
XP Pro
HP Pavillion
512 Ram
Celeron 1.2GHz

Any ideas would be appreciated.

Mike