E200 V2 not seen by USB drivers

[wongo]

I've listening to podcasts on my E280 V2 for several months.  At least once a day, I connect to my Ubuntu laptop and transfer/delete files in MSC mode.

I loaded RB on my E280 just before Christmas, using a development version, which version number is not now apparent.  Last week, I updated to version 3.5.1.

Yesterday when I connected, the device was not recognized.  When I monitor the system logs, there are no messages indicating insertion of a USB device.  Conversely, if I insert a thumb drive, I see several messages indicating insertion and subsequent configuration of that device.  In the past, I've seen messages indicating insertion, and then failure to configure or to load drivers.  In this case, I see NO indication of even the device being connected.  Running lsusb also indicates no devices connected.

Looking at the E280 screen, I see the normal startup screen when I plug in with the unit off.  It then displays "Writing" for 2-3 seconds, then "Connected".   The display shows device and computer, with arrows cycling between.  It also shows the battery, but no charge indication.

If I disconnect from the computer, the device reverts to normal operation.

If I connect when on, I see the charge indicator beside the battery icon for about a second, then "Writing" with no charge indication, then "Connected", as above.

I connected the device to a Windows computer, and see no indication on Windows that the device is connected.  Behavior of the device is the same as above.  Running USBView (USB enumerator) on Windows shows nothing connected.  The device does not appear in Device Manager.

I've connected the E280 to my Timex Sansa alarm clock, and all functions appear to work correctly.  I can navigate and play songs, and the device charges.

I've tried two different USB cables.  I've tried different ports on the laptop, all of which properly support a normal thumb drive.  I've tried putting the device in MSC, MTP, and auto-detect modes.

I would appreciate any advice on restoring the USB functionality.