How do I fix the video output of my Mac mini?

I bought this model A1103 mac mini used from a friend and when I brought it home it worked perfectly for a few hours. After restarting it the screen looked as if it were vibrating and about 10 minutes later the entire desktop has gone pixelated and high contrast with negative coloring. I tried restarting it again, no change, and I have tried starting it in safe mode, no change either. I also tried reinstalling the OS and it won't allow me be because It doesn't have an intel processor. Any ideas?