|When you first turn it on do you see anything at all--maybe the logo or posting screen? If so try booting to safe mode and lower the screen resolution.|
If it's giving a normal beep then the PC is probably OK and it's the monitor, monitor cable or maybe the video card--if you have an add-on card and your video isn't on-board. If you have added a video card try the on-board port as well.
If it's beeping differently the number and type of beeps will give a clue to the problem. You need to check the beep codes for your system or motherboard.