No midi output?

I have an AMD 2.7Ghz with 1Ghz RAM, running WIN XP Home and a SBLive! soundcard.
I used to play midi files quite a lot but haven't done so for a few months. Now I find there is no sound, but only from the Midi. Every other format works fine. I have checked the mixer settings; midi is available and the slider set to max with the mute unchecked. Have tried different midi engines all with the same result. Everything goes through the motions but nothing from the speakers. I tried restoring everything to default. I also tried A creative Diagnostics reset. Nothing seems to cure it.