K7N2 no video

[RonnieJ]

MSI K7N2 DELTA 2 MS 6570 VER.1
BIOS VER. 5.9
AMD ATHLON 2200+
RAM 1 GB
SAPPHIRE RADEON 9800SE
ANTEC 500w PS
WINDOWS XP PRO SP2

I have been running with this set-up for several years with no problems. All was well until a reboot, no video!! None! Nothing! I assumed it was the Video card so I put in a 9600SE. It worked with no trouble for a few days, and, with another reboot, no video. Installed an ASUS N6200TD/128/MA, still no video. I tried all three cards in another machine and they all function.
I dug into some old components and found an AsusV9280/TD/N/128/MA video card. This card I had quit using due to corrupted memory, lots of artifacts etc. I installed it and it works. I can get video to go into BIOS set-up, it displays the Windows LOGO screen perfectly but once booted into XP it displays at the lowest possible resolution, 4 colors I believe, and lots of artifacts, but it works.
The "D"bracket shows normal, all green, with this card. But with the other cards it displays red-green, green-red indicating a CPU problem. These three other cards have absolutely NO, ZERO, NADA, NOTHING as far as video display. No initial BIOS display..NOTHING!!
I suspect a bad MOBO but why does it function normally with the one card??
I have measured voltages, tried a different Power supply, tried a zillion different BIOS settings, but no positive results.
I have been trying to find schematics for the MOBO and general pin information as to what AGP pin is supposed to have what voltage etc. but have not been able to find any info.
What next??