General MIDI not working in Logic...?

[JumpingJackFlash]

For some reason, I can't hear any sound when I play a General MIDI instrument in Logic (Pro 7.1.1, on Mac OS X).

I'm just using the internal sound card that comes with the G5, and not using any external gear, not even a MIDI keyboard. MIDI works fine in Sibelius and QuickTime, but not in Logic.

I've been through all the settings many times, and for the life of me, I can't tell what's wrong. The settings are just as they were on an old machine of mine, but I can never hear any MIDI sound.

The Audio Instruments are working fine, just not the MIDI tracks. I can see activity on the MIDI monitor, the channel strip and the level meter, but not on the master Output faders, and there's no sound!

Even though I don't use GM all the much, it would still be nice to have it working, so please help!
Thanks.

[Cintronic]

do you have an au instrument loaded in thr midi chanel?