I sometimes have a very similar problem as yourself, which I find can be
cured by just restarting the system.
It doesn't happen to my computer very often, and to tell you the truth I'm
not sure why it happens, I'm just assuming that the drivers are not loading
properly first time every time.
In fact, it happened to my computer earlier this morning.
I just usually let it start up as normal (I can tell straight away when it's
going to happen), and then, if I can't see the start button(as sometimes
happens), I'll just press Ctrl,Alt & Del to restart.
So far this has worked every time.
Like I said, I'm not sure, but I would assume it's a driver issue. As in
your case, it happens even though no settings have been altered.
Hope that makes you feel better.(At least you're not on your own)
Michele Sayer

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