Happened once to me. Not a hard lockup so I did a Ctrl+Alt+Del and used the Sign out option. Then the power down and that got me out. On the next power up it worked. This issue seems to happen to a few and it's on the web.
Here's a thing I'm seeing. Folk today are demanding 110% correct operation. But the PC hasn't changed since say pre-2000?
Thanks. I ended up creating a new user, and that works fine. I think I can just delete her as a user, and re-create her account (saving anything that needs saving first) which should also work fine. Thanks for mentioning the problem is common and on the web. I googled it, and got the idea for a new user account from that.