My computer is rebooting at will. How can I correct this and what is causing it.

There is probably a virus attack.do a full system scan.if this is interrupted,try to reinstall the OS by formatting(only if u don't have important files on the system).
Another problem could be related to hardware,though it is far fetched.check all wire connections for loose connections.

While a virus attack is a possibility, its by no means a probability. You need to give us more info about what OS you have, how much RAM, what are you doing when it reboots, any error messages you get.