Probably an easy problem but I'll ask anyway...
 

Recently, every time I boot up the computer, the screen will go black for a second after logging on to Windows (XP). Then, when I go to open Mozilla, it'll go black for another second then come back on. I was just curious if anyone had any ideas. It doesn't do this at any other time while the computer is on so

I'm not convinced it would be a power supply issue. I don't really know that much about video card/monitor issues so maybe it's one of those?

Any thoughts?

Does it do it during heavy graphics/processing tasks? I had a dying PSU and it had just enough Wattage left for the basics, but as soon as I did something like play a full 3D game, it would start to turn off...

what video chipset do you have?

So far, it doesn't happen during gaming. Just on startup and opening the internet browser.

Really stupid question: there isn't a virus out there that can do something like that is there? I'm pretty much assuming it's hardware oriented...

if it didnt happen during gaming or other power hungry tasks i wouldnt assume it was a hardware thing. might want to try running antivirus stuff and spyware stuff. maybe uninstall mozilla and reinstall it. If all else fails try a full format and reinstall of windows.