We actually hadn't played for a while but just fired the game up tonight, and the microphone isn't working. It's the official mic (says Rockband on it). There is no power switch. The mic works fine with our Mac, so I don't believe there is anything wrong with the mic. We use to be able to play Lego Rockband with this mic just fine, but tonight, nothing I've done has helped. It's not picking up any sound from the mic. Further, I tried another USB mic (a Konami game mic) and it didn't work either. We do have a controller plugged in and neither mic has a power switch. Any help would be appreciated.

Make sure the mic sensitivity in-game is properly adjusted. If two separate USB mics don't work, then it's not likely that the mic itself is the problem.

It could also be the USB port on the console is somehow broken, so try a different port. Odds are, it's the game's sensitivity.

I will try it. Thanks! It's odd, though, if that's the problem, as I don't recall ever changing the sensitivity, but it is possible that one of my kids or nephews/nieces did. I'll report back on the result.

Alas, it's a no go. Even with the mic sensitivity set to the maximum it's not picking up any sound. I've tried 3 different USB ports on my Xbox. The drums and guitar work fine in those same ports too. :(

So you press start on the XBOX controller to enter a vocalist into the band, the player menu "pops up" but there is no response on the little level meter(s) on screen above that window at all when you make noise into the mic?

Does it even show the little level meter?

Actually I have this exact same problem with the mic that came bundled
with my Beatles Rock Band set. Within 2 weeks of use it quit working,
there is no noise level meter and no pitch recognition during songs.

The microphone I'm using currently I obtained from my friend's
original Rock Band set which he purchased for his now defunct PS3.
One major difference between the two is the plastic piece that stems
from the usb cord is much larger on the older RB set.
Whereas for The Beatles one it was completely shrunken down in size.

I still have the mic but it refuses to work, both in Solo and Harmonies. :(