I recently had the same issue with my USB becoming disconnected. I thought that I was out of the warranty period, but as this was the 2nd N900 I had purchased, it was still covered.

Thinking I was out of the warranty period, I rang Nokia to see what my options were, and to my surprise they offered me the option of an extended warranty.

I'm not sure they will always do this, but they are more likely to if you are JUST outside your warranty period.

Good luck anyway and hope it gets fixed without too much bother.