What make and model of monitor is it? Have you tried connecting a DIFFERENT monitor to the system? If you do, and the problem goes away, you have a MONITOR problem of some type, because the problem went with the monitor. If you have the SAME problem with a DIFFERENT monitor, you have a problem with your videocard, the CMOS settings, or possibly somewhere else entirely, because the problem stayed with the computer.
Truthfully, it sounds like a bad connection somewhere, whether it is the video cable from the monitor to the PC, or the videocard itself not fully seated inside the computer case. Has someone moved the computer or monitor recently? That can cause the videocard to lose full contact with the slot on the motherboard. If the videocard is not fully seated in the slot on the motherboard, you will not get a video signal to the monitor, and that would cause the type of problem you seem to have. If someone has recently disconnected and reconnected the video cable, you could have a bent pin inside the video cable connector, where it attaches to the computer. You might want to remove the cable and look inside the connector for a bent pin. Don't be concerned if some pins seem to be missing; DO be concerned if one or more pins are bent.
If you can, while using a different monitor, boot into Windows, then click on the Start button. Look along the Start Menu and tell us which version of Windows you have.
If you switch monitors and notice OTHER problems with the system, such as the wrong time or date, please make note of that and post it here.
