Dear pkr,
I have had the same problem several times. If you get nothing on the screen but the computer seems to be running correctly. It is definitely your video card. Either it died or the seating needs to be checked.
Have you added anything to your computer?
Have you moved your computer?
Have you cleaned your computer lately?
How old is your vid card?
Did you build the computer?
Also, when you check the seating of the vid card, please check the seating of all the rest of your devices.
Let us know if this helps,

Junkdk