volume control

[Robert]

Anyone out there with an iMic attached to external speakers and 
microphone. Since the  last upgrade to 10.3.3, I believe, the volume  
of the computer cannot be controlled. iTunes volume is controllable 
with its slider. I can also mute the sound with the keyboard but 
neither the keyboard nor the control in systems preferences has any 
effect on the volume. It  remains loud. When I disconnect the iMic and 
use the built in speakers which are woefully inadequate  I can control 
the sound via keyboard and preferences. I have trashed the sound 
preferences, run disk utility and corrected permissions. No change. 
There are references to this  problem in Apple's support discussion 
section with no solution.
Any other suggestions appreciated, Bob