Why does my computer restart when trying to switch users?

http://ift.tt/1iZHv9S

Windows restarts when second user logs on.

We have a shared PC at home and whenever someone else tries to log into their account, and someone is already logged on, Windows is just restarting, rather than letting the second person log in. I have tried Google but I can’t even find other people having this problem.

I have a fairly new (less than a year) Toshiba PX30t All-In-One running 8GB and an i7-4700MQ.

Any ideas would be appreciated.

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