If the mobile device has not been able to be detected by Windows even after cold boot and trying different USB ports and different communication cables, but it does communicate properly with a different pc, check the following:
In Device Manager, when the device is connected, it may show under Network adapters as "Microsoft Windows Mobile Remote Adapter". If it shows up there, but not under Mobile Devices or Portable Devices, then the connection information in Windows may be corrupt.
To force the device to redetect properly, on the device go to Start > Settings > Connections > USB to PC and uncheck the box for "Enable advanced network functionality".
On the HC1 Device, go to Start > Settings > System > USB to PC and uncheck the box for "Enable advanced network functionality".
If the device ever needs to be cold booted, that box will default back to checked, so it may need to be unchecked again to reconnect with the pc.