If you're getting no video at all, which includes nothing in Safe Mode, then it's probably the video card.. The easiest option is to purchase or borrow a PCI video card and test it.
Of course, swapping in new cables or even swapping in a known good monitor would help narrow the problem down.. If nothing works on the current video port, then you'll need to get a new one.
Hope this helps.
W XP Home, Sony Desktop (2004) w/I belkieve video off the MB (no separate video card), Envision flatscreen monitor. No recent software changes. I get a "No signal" msg. Checked cables, even took monitor to another desktop and it worked fine. Computer had been running really slow as of late. No AGP slot so I could substitute a known working card fm another computer I have. Thoughts?