Several KP's, then screen went strange?

I have a 2005 iMac, PPC. I've had several Kernel Panics in the last year, and finally replaced/upgraded the RAM. A few days ago, instead of another KP, the screen went all strange. The only way I can describe it is like when you pour paint on to a flat surface and it spreads out to the edges of what you're pouring it into. My screen went just about all one color: a light turquoise, which is what the background color is behind my desktop wallpaper.

I haven't tried turning it on since. I can't afford to go out and buy a new one, so I have to try and repair it to the best I can. I have a little Linux netbook which I'm using right now... but it can't do everything I do on the Mac. Help? I think it's the logic board, but I'm not sure. When I ran hardware tests from the CD, it froze on the Logic Board. Am I looking in the right direction? Where would I get a new LB, how do I know what to look for?