I can no longer tether my n900 to the laptop via USB. Laptop OS (Windows 7) says I get no dial tone, so it can't call *99#. This used to work! Sigh. I'm in the US, carrier is AT&T.

I wonder how to troubleshoot this. I guess the first thing is to figure out if the problem is with the N900 or with the laptop. Is there an app for the N900 to issue AT commands?