If you have administrator access then get into the device manager and uninstall the Droid. Once you've done that, plug the phone back in. You may need to install the latest Motorola drivers. Heck, if you have admin access, just install this, use it to clean out the old drivers and install the new ones.
http://www.motorola.com/staticfiles/..._bit_4.7.1.zip
Unzip it, install it, then clean out the old drivers, reboot the PC in question, then install new ones, reboot (one of these reboots is unneeded, but this should help make sure it works the first time), then plug the phone in. See if that helps.