Ugh, I have this happen from time to time, no clue why or what triggers it.  

When I hit Switch To, the Windows Start button menu opens and then I close it, then I have to hit Switch to again and the same thing happens...usually does it 4-6 times in a row then everything opens normally.

The only thing I can think of is maybe my anti virus or my cloud back-up is doing something with the PS files at the same time as Im trying to log in and its creating a conflict?  I honestly dont know what to tell you, except youre not alone!