screen starts flashing colors, goes black, becomes unresponsive?

When I was using my computer, the screen suddenly when gray, then starting flashing colors (Red, Green, Blue, White) then would eventually go black. The computer became unresponsive but I could still turn on/off the caps lock key. I did a hard restart and it worked fine for a while but before long the same thing happened again. Since then, it was completely unresponsive for a while (couldn't turn it on by holding down the power button) and it has worked for a little while if I take out the battery and hold down the power button for a while before trying to restart it. I've also tried to reset my PRAM and PMU, which seemed to help for a while but eventually this same thing would happen again.

Is there anything else I can do? If I can get it up and running for a while again, what should I do to prevent this from happening again?

I don't have the software disc to boot off of, but I could get in a few days if I really have to.

Thanks, I'd really appreciate any advice I can get!