IMac screen on start up flickers

On start up the top half of my screen flickers for about 5 minutes and then goes to normal. Is there a setting to correct this or should I be looking at replacing the video card. I am running OS X.4 and it is the Summer 2001 DV 500 mhz processor. If I need to replace it I have an ATI MX4000 (AGP) with 128 meg and wanted to know if this would work. Also is there a reset function for the video card?
Message was edited by: SnkEys990

There is no physical video +card in a slot+ in the iMac, so you cannot replace it. The video chips are on the motherboard. The problem is probably not in those components anyway. If there is a video problem, it is more likely to be in the analog video board that controls the CRT. These iMacs are CRT monitors and computers rolled into one package, and the CRT-video portion is often the part that fails, not the computer-video portion.
Here's something to check... Although the CRT of iMacs degauss when the iMac is started or restarted, this document
http://docs.info.apple.com/article.html?artnum=25339
says you should leave the iMac off for an extended period if it is continuously turned on.

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