midi keyboard works /doesn't work

Trying to figure out what I'm missing here. Keyboard worked briefly on a measure, then stopped working. the mouse over rides note input. Sound from keyboard stops. Everything for midi connect looks correct-- keyboard is connected -- in preferences midi input is selected, in I/O the keyboard is there and selected. The midi icon in the tool bar is highlighted. When I hit "n" or click the N in upper left for note input it seems to default to mouse input rather than midi keyboard. I hit N and a note appears right under the mouse arrow. Once or twice the keyboard suddenly worked for note input then stopped working and the mouse took over. Any suggestions?