How do you have it connected?
That is, working backwards, at least to the preamp (I'll assume you've got mics connected to both channesl of the preamp, and they're actually amplifying something):
- What are the inputs to the computer?
- What cables are plugged into them?
- Where are they plugged into the preamp at the other end?
Also, I'm not sure I follow the question. When you say "only the left channel works," it's not very clear what you mean by "works" (or, more to the point: "doesn't work," insofar as that applies to the right channel). Apparently the right channel of Audacity is working, since you say it's recording something.