Operating on Windows XP 2003 Home Edition Service pack 3

Okay, so I'm not exactly sure what's going on here, but as the title describes, my computer loses visual and goes completely blank from time to time. What do I mean by blank. I mean that the monitor is on, but there is nothing coming from the machine and going into the monitor. The monitor is still on though, and I know this because the speaker attached to it has  a little blue light in it that turns on when then monitor is on, and that stays on during the BLACK out. When it happens I can't get it out of it unless I force shut it down by holding the power button.

Most recently however, while I was booting back from safe mode, the monitor alternated from completely off to blank. The computer never FINISHED booting though, and I know this because when the log in screen appears, the fan turns on and the computer makes lots of NOISE. As the screen alternated from on to off, the fan never turned on, and even though I couldn't see what was happening, I had a feeling it never made it to the log in screen. I'm not going to jump to any conclusions but I think this might be some sort of system hang.

I noticed this start to happen about three days after I had forgotten to install my system updates for about two weeks and when I finally installed them this happened. I scanned my computer (most of it) and I didn't find any viruses, however it might have been invalid, as my antivirus avast! doesn't know how to update anymore because a blank screen happened in the middle of an update and screwed something up. Right now I'm on the wonky computer, as it is my only computer, and it's doing good so far.Could be a variety of things that could cause this to happen. Worst case scenario you graphics card is failing.I would suggest you try a few things to see if you can change the outcome.
1.temporarily disable your virus protection and see what happens.
2.remove all but one of the Ram MODULES and then one at a time try them in all the slots. Once you find a single one that (if) runs properly then ADD the others one at a time to try and find one that is possibly causing this.
3.Try another cable between the computer and the monitor.
4.Try another monitor.
5. Install another video card.
6.Do a restore on the computer to a date before the 1st instance of this occurrence.
  After doing these things report back as to what you found, truenorth