First try to borrow a friend's monitor and connect it to make sure that it's your monitor that's the problem. This might sound obvious, but make sure you haven't accidently turned the screen's brightness right down. That could give you a blank screen.
A replacement monitor is pretty cheap to buy, if that is indeed the problem. It's probably not worthwhile messing about with getting the old one repaired. You may be able to get a very good cheap one if you take the time to check-out ads for second-hand stuff and, of course, EBay.
It doesn't have a to be a Dell replacement. (We've got a Dell PC, with a Philips monitor and Logitech wireless keyboard and mouse)