My mother's iMac G5 began this just two days ago. It turns on fine, but once is reaches the apple logo with the spinning wheel, the screen begins to exhibit what is shown in the pictures below. It first started when I opened an .AVI I received in an email from my uncle. When the file opened, the whole screen(within about 2 seconds) had discoloration and macro blocking spread from the center of the screen outward. After this I rebooted, tried again, and when I opened the file, it did the same thing. Now I can not even reach the log in screen. And after the screen has been in this state for a while, it may go blank and the fans run at full blast. I've opened the same file on a PowerMac G5 and a MacBook Pro with no problems. Can anyone tell me what may be wrong?