I am following your approach, and it works to restart the phone without disturbing anything. It seems the phone is going into a estate of disconnection from the USB port. The PCs or Win OS tablets do not recognize the device and cannot synch with it. The wall outlet charger appears to lock out and may not charge the phone. A PC rear USB, where most the power is at, appears to boot up the device and charge it. I am under the belief that a software update is causing the problem. While many are suggesting to flash the phone with the recovery tool, it may do more harm than heal.
The issue is the USB is disconnecting and not synching with any device; it is what needs to be researched and shared for all of us who remain in the windows mobile platform.