On some customer's computers, we have observed an issue where the "Windows Mobile-2003-based device connectivity" and "Windows Mobile-based device connectivity" services stop after a device disconnects and revert to Log On as NETWORK SERVICE, preventing the mobile device from being properly recognized to connect with Windows Mobile Device Center.

Should this occur on a regular basis on your machine, you can download this file to your desktop, and then when the services need to be reset, right click the file and select Run As Administrator.

http://dl.waspbarcode.com/kb/mobiledevice/RestartMobileServices.bat

When run, the file will issue a stop command to both services, set them both back to Log On as Local System, then issue a start command to both services. This should only take a few seconds, after which you can re-open Windows Mobile Device Center and reconnect your device.