|3 long beeps is keyboard error. |
It's an ancient IBM beep code. Intel made most if not all of IBM's mboards in the beginning.
A PS/2 keyboard has to be plugged into the purple PS/2 port properly. If it's not all the way into it's port, push it in ONLY when the computer is not running.
If you are using a PS/2 keyboard, if that doesn't help, try another keyboard - PS/2 or USB. It's common for wires to get broken inside the cord of corded keyboards, often right where it enters the keyboard.
If it had been 3 short beeps, grasshopper is is right in this case - ram error.
BIOS beep codes
3 beeps - Base 64 K memory failure
Reseat the memory.
Make sure that the contacts on the memory and the socket are clean.
Try removing one bank of memory modules at a time. Note: Some systems might need to have a memory module in Bank 0.
Try using memory modules from the same manufacturer with the same part number and speed.
Check for a faulty memory module by trying the memory in a known good system.
Trying known good memory in the system.
Check the power supply and check for power fluctuations.
If the steps above do not resolve the problem, the desktop board may be defective. Try a different desktop board.