Restarts itself after shutdown

My friend's Toshiba laptop today started doing something odd. When he shuts down the computer in either of the usual ways, the screen says Shutting Down, and then goes black, and immediately after that boots up again, starting with the Toshiba splash screen.

Any ideas what might be doing this?

Thanks

BTW when he forces a shutdown by holding down the power button, then it stays off.

Mine started doing this after updates. I don't know which one is responsible.

My friend tells me that the forced shutdown seems to have fixed this issue. It is ok since I had him do that.