Desktop

The beep is a "POST" error.
Power On Self Test

1 or more pieces of hardware fail the initial test that the BIOS performs before starting up the PC.

Please describe the beep noise.
Continuous beep,
sequence of beeps repeating
solid tone
warbling "alarm" tone

Also include details of what your PC is.
Make model, motherboard etc.

That way, we can help you find the POST code meanings for your system.

I suspect that the system is not detecting your video card.
Most likely, the card has slipped out of it's socket in the motherboard just enough to loose contact.

It could also be bad or loose RAM modules.

The first step, is to open the case, and re-seat all plug-in cards and RAM modules.

If the noise is closer to an alarm tone, the motherboard monitor circuit is either not seeing the CPU fan, the CPU fan is spinning too slow, or the voltage for one of the power supplies is out of specification.

Chas

Lots of continuous beeping?
Make sure the video card is properly seated.
Regards, Chris

The beeps are like 5 quick short beeps right after each other.

The computer is a Emachine 550, 550 MHz, Pent. 3 and I not sure about the rest.

Silly question, but are you sure the monitor is plugged into the correct place?

The 5 beeps indicate a motherboard or processor malfunction. Attach is a link on how to determine.
http://www.pcguide.com/ts/x/comp/cpu_Failure.htm