C-Media CMI8738 PCI Sound card issue...

I have a C-Media CMI8738 PCI Sound card. My microphone input is too low. I can only faintly hear the mic through my speakers. If I turn on the mic booster in the C-Media mixer software, the mic volume is louder, but I get a very loud squealing/buzzing noise mixed in. I have disabled my on-board sound card (the buzzing is there with the sound card enabled too). If I unplug the mic, the sound is still there. If I turn off the booster, then the squealing/buzzing goes away. The mic is ok. It works fine on another pc. I've also tried another mic and I get the same results.

I have Windows XP and the sound card drivers are up-to-date.

Any suggestions?

Thanks,

-todd