Sometimes I have had to try several times to get the flashing to complete. What do you mean by "nothing happens"? If you have version 1.70 still running on it, then presumably you can flash it via WiFi? That is less tricky than USB flashing. If version 1.70 no longer runs, then you can connect to a USB-serial terminal program and see what it says (if anything) after you press the reset button? If there is anything connected to Pin 2, disconnect before USB flashing. Try the "erase flash" action in the flashing tool, that will remove anything in the flash that may be interfering with the firmware flashing. But only after v1.70 no longer runs, otherwise WiFi flashing is better option.