Help, my computer has stopped shutting down. When I click on shut down it reboots every time. The only way to shut it down is by the power switch which is a bit dodgy. Any ideas? I am not aware of making any changes to the set up or bios.

What is the make and model of the computer?

If this is a new problem System Restore is always an option:

start > all programs > accessories > system tools > system restore

Choose a date prior to the issue.

Here is a good article that can help you figure out what is happening. Troubleshooting Windows Shutdown Problems

Most likely you are getting a error at shutdown that is causing Windows to restart. The above article will help you turn off auto restart so you can see what the error is and then fix it.