« Reply #11 on: Saturday 19 May 18 19:15 BST (UK) »
Does pressing CTRL + ALT + DEL together not take you to another screen with the option to sign out (among others), or at the bottom right a power symbol (as well as others) which should give you the option to shutdown? You will probably need to press all three for a couple of seconds rather than just momentarily. Sounds like your login profile has been corrupted or renamed by the upgrade. Is there another login account setup on the PC?
Pressing the power button runs the risk of corrupting windows further, but if all else fails there isn't much else you can do.
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