turned on comp fails to wakeup monitor

About 1-1.5 sec after turning on of my comp it BEEPS for about 2 sec and the ontinues to function, but it does not turns on the monitor (black screen). When I try to connect to the comp via LAN, I have no problem it functions correctly. I check the monitor it is OK. I replaced VideoCard GeForce FX 5200 with another GeForce card (checked to be OK), but again, I got the same. When I unpluged a VGA cable from the video card I got “no signal” on the monitor. The monitor is all the time in stand-by. I tried to turn off and on ot and I got black screen and the monitor went to stand-by.
Anyway it is not Windows drivers problems since I do not see anything including BIOS loading.

Any idea? please and thank you