When booting computer I receive several beeps
Keyboard has a stuck key
Turn off the computer and temporarily disconnect the computer keyboard and turn on the computer. If the beeping does not occur when the computer keyboard is disconnected it is likely that a key is stuck or that the keyboard is bad. Slapping the back of a keyboard to dislodge any dust, dirt, or hair may help ensure there are no stuck keys on the keyboard.
Computer has a password
Some computers have the capability of having a BIOS keyboard password. This password will sometimes cause the computer to beep and the keyboard not to work. To determine if this is the case look at the keyboard LEDs (Num Lock, Caps Lock, or Scroll Lock) if these are flashing continuously the computer has a password.
System Chassis alarm
A beeping or buzzing tone can also be caused by the system chassis alarm also known as the intruder alarm when the system case is removed. Verify that the beeping or buzzing noise does not also occur when the computer is off. If this is the case remove and cover of the case and then put the case back on.
Computer does not pass POST
The more likely possibility of abnormal beeping is when the computer does not pass the POST (Power On Self Test). When the computer fails this test it will sound a 'Beep Code' indicating what caused it to not pass the POST.