The simplest solution i have found is to make sure HTC Sync manager on the PC is of the same version the phone is looking for. Looks like if the versions are different the phone does not get detected.
To do this:
1. Uninstall any existing HTC Sync Manager softwares on your PC completely
2. Connect your mobile to your PC
3. In your phone, in USB options choose "CD Installer" instead of "Charging" or "File Transfers"
4. You will now see an image of HTC Sync Manager mounted on your PC. Just follow the standard instructions and install the HTC Sync Manager software
5. Launch the HTC Sync Manager software now. Disconnect and Reconnect the mobile
6. Phone should now be detected
Let me know if this works.