Now, here's a thing!
I have the same problem from time to time, I don't know what mis-key or keys I hit to start the problem, or which correct sequence of events eventually sorts it out, it just happens without my apparent direction.
Well, it might even be the start key.
When the cursor went white, it allowed me to see a tiny vertical line just to the right of the Start button. Remember, the button is two lines big - and round.
I simply pulled that line LATERALLY to the RIGHT. PRESTO! everything back to normal. Opened progs now contained
within the taskbar, and the Start button is now small and rectangular, being contained in one line. Thingies on the right are now obviously all on one line.
Now all I've got to do is find out how to turn the background of the bar to black again.