Windows 7: Restart without warning after login, only after fresh boot

So I've just installed a fresh copy of Windows 7 on this iMac, I am getting an instant automatic restart as soon as the user profile gets logged-in.

The strange thing about this is that after it has gone through the restart process, it will log-in to the profile just fine and you can use the computer as normal.

How can this be happening? Is there a difference to the OS whether you have just logged in following a reboot OR fresh boot? Surely not?



I need to have a play around with it to see what is causing it, whether it is related to this specific user profile or not. Although this is a brand new install with a fresh user profile so it shouldn't make much difference.

Any help much appreciated.