How long is a piece of string?????
First check your video cable from your PC to the monitor. If that is OK, and you have video card (A card plugged into your mother board that the monitor plugs into) remove it, clean the contacts with a soft pencil eraser and replace.
If still not working, take out your RAM and clean it /them and replace.
If that won’t work, unplug your hard drive, CD/DVD drive, 3 1/2 floppy, keyboard and everything else other than your mouse and monitor and see if monitor gets a signal then.