video garbage on start up / restart

Folks:

My G5 has suddenly begun generating what I want to describe as "patterned screen garbage" when I start up and/or restart the machine. This seems to be slightly less intense as the machine warms up. Sometimes it is so bad that I can't even see the sign-on box. Other times I can get started and signed on, and matters gradually seem to resolve as I begin running programs.

Hardware details: G5 dual processor, 2 ghz, built 2003; 3 gb ram; Original 30" Apple Cinema LCD display; Radeon 9800 XT, R360 graphics processor.

I ran TechTools once I got the machine up and running, and it found no problems--but of course that was when the video was working. (I tried to run it when the video was weird, but could not see enough to read the report.) I also tried to search the web to see if this was a problem, and found nothing. Have done obvious stuff like checking connections, unplugging peripherals, etc.

My thoughts are that this could be a bad graphics processor, display, or RAM chip. But I wanted to see if anyone had experience with this kind of off-again-on-again graphics issue, especially on start up and restart.

Thanks for your help,

Bill Poole