I have two Optiplex 755 tower Core 2 Duo 2.0 GHz.

one is okay.

the other would abruptly send a blank video display in the middle of BIOS screen on monitor.  Issue happens with both integrated VGA port or PCI video card.

I tried reset CMOS jumper.  Does not help.  Sometimes video display comes back after I change RAM or mysteriously, then disappears abruptly again.  It disappears right before I exit BIOS and try to save changes.

Does this mean a faulty motherboard or BIOS?  Even when video is blank, I heard the POST beeps telling me floppy drive not found(because I removed floppy ribbon cable).