Computer alarm beep

how much beep do you hear when he restarts ?

It beeps the entire time it is on.

Take the memory out and switch your pc on, it beeps and stops, then board looking ok as it detects no memory found, then add a stick at a time until you find the dodgy stick.

FYI, 1 long and 3 short beeps is video card.

sounds like a fan failure to me....

Try this:
http://www.intel.com/support/motherboards/desktop/sb/cs...

What is the system you are using, please give the complete config.  

the siren sound is often a graphics card telling you it isn't getting enough power.

make sure that your GPU is correctly seated, and that its PCIe connectors are in (if it requires them)

this seems most likely given what you have described.