Dude - at some point, you probably tweaked your settings in your BIOS after reading some funky article online or in Maximum PC. You probably turned off stuff like AGP Fast Write and other special video settings thinking you would get one nanosecond cut off of your processing times or one extra mflop.
That was the case with my PC. I fought this black screen crapola for weeks and no one could help me.
Go into your bios on boot by holding down DEL, and then see what video settings you have, and restore some of the defaults, and the black screen will probably start working.
On mine, I had disables several video capabilities of the video card.
To test to see if this is the problem. assume the black screen is a logon prompt you just cannot see. Type in your user ID, hit ENTER, and then your password, hit enter. Then type startx and hit ENTER. If X starts, and you can see it, then your video card settings in the bios are the problem.