Sudden incompatibility between Asus Motherboard p4s3 and Asus v7700 video card

Hi all, a friend of mine take his PC to me to solve OS problems, but
when he came here, the problem was that no video signal arrives to the
monitor. The same pc works fine with another video card, and so does
the video card on another pc, but they don't work together.
This PC worked with no problems for 2 years, so it can't be a
"genetic" incompatibility...

I read many posts on incompatibility problems with Asus motherboard
and geforce video card, but i can't find any solutions on my specific
problem. Can anyone help?

This is the configuration:
MB: Asus P4SE rev 1.11 (Bios rev 1011, just flashed from 1009)
CPU: Pentium 4 1800
Ram: 2 x 256Mb
Video: Asus V7700 deluxe
Audio: SB Live!
Modem: unknown 56k internal
Drives:
Prim master: Quantum Fireball AS 40
Sec master: DVD-ROM 16x (unknown brand)
Sec Slave: CD burner Lg 16x10x40
Floppy

there is also a Asus S/PDIF OUT module (i guess)

Any help or suggestion would be much appreciated!
Bye

Wil

PS I'm not very used to newsgroups so if this is not the best place to
ask, just give me directions: i don't want to bother anyone