Problems with my computer starting

Hello,
when i start my computer i can hear everything running, but right away my monitor says "no input signal" and then just a black screen, but still runs...any ideas??

Have you checked the video cable?
Do you have more than one place to connect the monitor, and did you try them both?
What did you do right before the problem started?

You have some sort of hardware failure. It might just be your video card (if it is a separate card), or it could be something worse. It is hard to tell without more details.