PC monitor shut off and PC beeps every 3 seconds.

So I went in to the other room for 5 minutes and started hearing beeps from my e-machines computer every 3 seconds. When I went to look the monitor was off but the power light on the PC was on. I then shut down the PC by holding in the power button. When I turn it back on it just beeps right away and continuously about every 3 seconds. The monitor never turns on and the computer is beeping every 3 seconds. Can anyone help me?