I had a similar issue (though not as severe) whilst using an ECS (Especially Crappy Stuff) motherboard (which had onboard VGA) and a graphics card. Once I installed the graphics card I couldn't see anything on the screen until the Windows logon prompt came up!
To configure the card I first had to go into the BIOS with the card disconnected, setup the BIOS, as if a card was connected - shut down, install the card, then start up! Long story short not an ideal arrangement, but I have no doubt the motherboard was at fault.
Have a look to see if you have an ECS motherboard, if you do take it out of your computer, throw it on the ground, get a hammer, smash the board, pour flammable liquid onto the board - set afire, etc!!!
But really if you have a graphics card installed but your motherboard has VGA onboard I suggest taking out the card and seeing how the computer behaves. In all likelihood it is the motherboard, but there is a small chance that the graphics card is causing you some grief!