I'm assuming he's talking about the "No Signal" meaning it is not hooked up...
Ok - this just happened? The computers worked fine yesterday?
Try to interchange the monitors, see if anything works.
If you are sure this monitor works, shows blank at startup and you get one beep, the chances are that your video display circuitry is defective. Your video card is probably a dud. If you can, try another card in your computer.
Did you recently switch your ram?