Computer keeps crashing??

This started a few days ago. The computer would freeze up, then slightly change the colors of the desktop or program opened. The screen has done a stobe effect for some of the times. After I shut the computer down then try and restart it, it looks like it is about to start then a grayish screen comes down that say you need to restart the computer. Everytime I restart it says the same thing. I found a way to finally get it working by using cmd + s and fsck -fy at the start up. But eventually it begins to crash again and I have to go throught the process all over again.

I have a Macbook Pro Mac OS X 10.5.8. Have not had any trouble wih this before. Any ideas on how to fix the problem or even what the problem is.

Also at one point when i got the computer back up it stated that Mac Os X failed and that was reason the computer needed to be started.

Thanks!