Originally Posted by Soundteq
This has happened to a lot of different devices for me, but never a phone. However I've always fixed it the same way. In your hardware manager, go up into one of the toolbar options (I forget which it is, but it should be easy to see) and select "scan for hardware changes". It will say "scanning for plug n play compliant hardware".
This usually does the trick. Sometimes it takes no time flat, and other times it takes like 5 minutes =\. Occasionally it will not recognize the device or it will freeze up, but just close out and retry.
The computer could not see my HTC phone and ALL I had to do was go to the phone settings on the phone and click "connect to computer" its so easy!
I hope this helps!