monitor goes dark??

Moved system to another room at home and now this is happening.
When winxp starts, the monitor works fine. About 1/2 way through startup the
monitor goes dark and the green 'on' light flashes.
I had to shut down power and restart. scan disk starts and after running
through to 100% and giving detail of scan, monitor goes dark.

Even though monitor does dark, the system keeps starting. I hear the little
MS gingle, the HD keeps running, etc.
The only thing I did was replace the LAN card with a wireless card. When
this started I removed wireless card.

I can't get into SAFE mode. Hit F-8, safe mode and system tries to restart
in normal mode.

Any suggestions please,