I recently upgraded my (Windows 7) development environment to Eclipse 3.7.1 (Indigo). I have an HTC Magic (Rogers) running Android 2.1upd8.1, a Kobo Vox running 2.3.3 and a Samsung Galaxy Tab 10.1 running 3.1. Only the Galaxy is visible as a USB connected device. [Previously, under helios and Ganymede, I had no problem finding and testing on the HTC! Also, I have no problem executing on any compliant virtual device under the current indigo setup.]
Does anyone have any ideas what the problem might be with the HTC and/or the Kobo Vox?
I recently had a problem with my computer detecting my HTC Desire after upgrading. I switched USB ports and now it detects it.
You can also try to update the software on your pc.