If your alarm is going off then its most likely overheating... I would suggest installing something like motherboard monitor to check your temps also check to see if your fans are working... You dont want it to overheat too much you can seriously damage your cpu.
Try opening the side of the pc to get air into it and open some windows.
If its like a siren then cpu over heat, your fan has prob failed, i owuld recomment u get a new one asap as cpu could be damaged by over heating. when set right pc should shut down, must be disabled the cpu protection.
my friend just popped in (luckily) who knows about pc's, he went into the set up and he said that the temp is disabled, so he enabled it. The tower is inside a 300mm kicthen cupboard but with the back cut out, so i've opened the door and it stopped after about 5 minutes. It did feel pretty hot in there so i'll have to install an extra fan inside there. thanks guy's.
Now Red, where's that bloody egg?