Problem just started happening.  The mouse will wake the computer but the Logitech K400 keyboard will not.  When computer wakes, there's no keyboard connection and the Logitech Unifying software doesn't see any keyboards.  If I unplug the Logitech Unifying receiver USB Key, and plug back in, I get a windows message that the last USB device plugged in was not recognized (no matter which port I plug it into).   I have ran the update driver routines on everyting.  I've used Device manager to ensure all USB devices' (including hubs, mouse, keyboard) power management is set to not allow windows to turn of and/or 'allow this device to wake computer' is set (where applicable).  Have deleted all hidden USB devices.  Have disabled USB Selective Suspend in power configuration. Keyboard works fine if I reboot.   Pulling my hair out at this point.