Dell Optiplex 3020 won't turn on

I recently received an dell computer it won't boot up. when I plug in the pc into the power supply it only comes on with a amber light at the power button that flashes once then turns to white which also flashes once then the systems reboots. sometimes the amber light blinks 4 times before the white light appears and then reboot, also a single beep is heard before it reboots.