You should be running an Award BIOS and a single repeated long beep indicates your CPU is overheating click here
With all power turned off you should open the case and check the CPU fan will rotate and is correctly plugged into the right socket at the top of the motherboard. If it is solid/stiff you need a new fan.
Make sure the heatsink fins are not blocked with fluff/dust. A small paintbrush and vacuum cleaner can be used but take care not to spin fans when vacuuming or to do any other damage.
Also check the heatsink/fan assembly is not detached from the CPU - it should be solid; no movement at all. If it moves it is likely the thermal paste/strip bond has failed and needs replacing.
If the above is all OK turn on power and check the CPU fan spins up. DO NOT put fingers or tools into the case with power on.