| | Probably a physical problem
This has been discussed elsewhere on the forums, and it appears to be a physical problem with the handheld USB port or cable. I'm having the same issues, and can only seem to connect if I apply sideways pressure in a particular direction to the cable end where it enters the PC (same problem on all USB ports on the PC). I plug it in and out while applying such pressure, and if you get the USB connection beep and the "device password" login, you know that for the time being it's connected. Then I have to carefully maintain the pressure until I've done what I need with Desktop Manager (with one hand!). Of course, this is no good for charging, because you'd have to sit there for hours. Also, if you opened DM and connection was unsuccessful at first, DM may not see the device even after you have a good physical connection. So you may need to close and restart DM. Naturally, the PC end of the cable looks completely normal, so I'm not convinced that replacing the cable would help, although that's the next thing I'll try.