I'm not familiar with the Maxtop case.  Did you check to see if the power
supply that it comes with is on AMD's approved list for the XP 1800.  You'll
need to examine the power supply to see what brand and model number it is
and then look it up in the list on AMD's site.

With regard to the possibility of it being a video issue, make sure that
your video card is securely seated and that the fan on it is working
properly, too.  (Rereading your note, I see that you probably already did
that.)

Some times it is possible to troubleshoot heat being an issue by simply
opening the case and blowing a house fan into the innards to see if this
helps any.

Good luck,

John

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