If you have tried all the usual thing like cleaning the charger port, holding the 3 buttons together, booting in SAFE mode etc, you may want to try this out. Connect the HTC One to a 'multiple USB connector' (google it if you don't know what it is) and then connect that to a notebook. That works for me. By indirectly connecting it to the notebook, it seems to be able to kicks it out of USB mode.