I downloaded a trial version of Keyboard 2.4, a music program, yesterday. I was messing around with it in between real work, and after about the sixth or seventh time I opened it - no music. (For the uninitiated, it turns the computer keyboard into a piano keyboard.) I thought this was a pretty nasty way of coercing me into buying the full version so I ditched it and downloaded a similar program called Piano 4fx. I've still got the same problem - no sound.
The comp is making all the other sounds as usual, and the music player is fine. I can't connect this problem to anything I've done except install a new cordless keyboard - Logitech EX110. I'm going to see what happens when I set up the computer's original keyboard, but apart from that has anyone got any ideas?

Uninstalled, reinstalled - problem fixed. Interesting how these products offer you an option on which features you can install, but don't explain that not installing them may mess up seemingly unrelated functions. In this case I had chosen to not install the music player option. Now that's in and we're all one big happy family.