There are a few possibilities:
Your Graphics Card is broken, or somehow it's killed itself.
Your monitor is broken, or somehow it's killed itself.
What did you do in the week before it happened (if you can recall):
Did you use any driver-intensive applications?
Did you open the case and poked your card and/or motherboard (hopefully not)?
Did you install any software (drivers, files, antivirus etc.)?
You didn't really give any detail, just the problem, and even the problem wasn't described in detail...
It's like taking you ring up your local mechanic and tell him your car broke down, but you didn't say when, where or what happened.
More detail please