Well plug the monitor in then, and turn it on. Just kidding.
Did you do a bios beep code test?. What I mean is if you turn the computer on and hear a single short beep then the computer is saying it is ok and all the hardware inside is working right. If you you get any other beeping it relates to a hardware problem.
Please look up bios beep error codes to locate your problem. the other thing to check is if the video cable from the PC is fitted in the right place to the pc monitor.