Can't control highlighting in Edit function

I’m using Windows 7 and have been using Audacity 2.0.3 regularly. I do voice over recording and when I go to edit portions of the tracks, the function to highlight in Edit (to control small portions needed to cut, copy or paste) has stopped working properly. It does not let me control the sections: just jumps forward, back or sticks in the track or washes over a large section. Thought it was the mouse, but mouse is ok–it works fine everywhere else, except this one function. This just happened yesterday, and I find no reference to this problem in the Forum! I’ve got a lot to work on, and cannot go forward. Thanks in advance.

Please see .