Beep code and nothing on monitor

Question

When power is turned on all I get is a long beep repeated every few seconds and nothing on the screen.  I hooked the screen up to another computer and it works fine. I unplugged from the motherboard what I think it the power supply (wires in a bundle go to the power supply and also to all the drives.  Any ideas?  If I could only get info on the screen I may be able to fix it, lol.  Thanks in advance for any help you can give.

Michelle