try reinstalling htc sync? you'll need the correct drivers installed (via HTC Sync) in order for your computer to recognize the phone. When I was rooting my phone, I made sure that my phone could connect to HTC sync. Then I went on to root it, and I've never used HTC Sync again lol.
Hello I have some useful info for you. Android Debug Bridge | Android Developers
[HIGH]Server start-server Checks whether the adb server process is running and starts it, if not.
kill-server Terminates the adb server process.[/HIGH]
I did research awhiile back. Will need HTC Sync program from HTC for it to work / install drivers.
or Task manager to kill adb.exe you can try that one too.