Video died, but it's not a dead videocard, or monitor

Last night, my secondary system's (Athlon XP 3000+ with a
6600GT AGP) display just went black. I had the system up, & running my
personal Shoutcast stream server, and nothing else. I was listening to
one of the stream slots over my lan from my main system when I noticed
the display of the secondary system just slowly "disappear" into a
fine vertical line, and then blank. The system was fine as the stream
kept going, and doing "blind typing" commands let me close the stream,
and shut down the system.
I first just tried doing a power down reboot. No display. I
then figure the CRT must have died as it's an old 17". To make sure, I
plugged the CRT into my legacy Pentium 3 system with it's Voodoo 5
5500, but it works fine. I then think the 6600GT AGP card must have
kicked the bucket, but I installed a working GeForce 2 MX400 AGP, and
there still is no display. So both the monitor, and videocard are
good, then does this mean the mainboard's AGP slot is dead?