There's a sticky in the LE forum about using USB mics. Maybe you find useful info there. USB-mics can be a real PITA because they are actually soundcards, and because many of them don't offer all necessary functions and/or don't have good drivers, you need to use your mobo soundchip as well. Then, using two soundcards leads to many kinds of problems regarding clock sync etc.
Make sure your USB-mic is selected as both record and playback timing master.
SONAR PE 8.5.3, Asus P5B, 2,4 Ghz Dual Core, 4 Gb RAM, GF 7300, EMU 1820, Bluetube Pre - Kontakt4, Ozone, Addictive Drums, PSP Mixpack2, Melda Creative Pack, Melodyne Plugin etc.
The benefit of being a middle aged amateur is the low number of years of frustration ahead of you.