Screen lock

I just tried to make a little score, nothing major. I got to first in the second measure, no more notes appeared, I get a cursor that is an up arrow, no notehead and once in a while I get a sound but still no note appears in the score.
The bar line is highlighted, and the last note is highlighted. It will go away after I reopen MuseScore, but not is what I want to do every time. MuseScore 1.1 Windows Vista.
I tried to make a screenshot but the cursor did not appear in the capture.