Sonar LE - Recording from CakeWalk Sound Center

Help - I'm really new to this! OK - I've read the manuals but I'm obviously missing something basic.... I've got LE up in the background; I've got nice Sound Center keyboard in the foreground. I've found a nice sound which I want to record on a track that I've opened in a new project file. I'm using the mouse to play some lovely sounds. All the relevant record buttons are pressed and the track view moves as you'd expect to.....but nothing actually records. When I input manual midi notes using DropZone it worked and they played back. But now nothing. It's really doing my head in!!!! HELP.