also make sure its set in digital if you have digital or analog if you have analog. not all monitors have this but mine did and it did the exact same thing when i first got it, scared the *bleep* outta me.
it varies w/ diff models if the other suggestions havent helped you enough. check the manual it came with.
if its an old screen that used to work it may be your GPU
*edit* ok if happend after the new drivers were installed, the drivers probably set your vid card to some crazy option that the monitor doesnt recognize, boot in safe mode and tell us if that works