I was using the Arduino Nano as a voltmeter which would output its values through its serial monitor. I can't remember exactly what happened, but I remember I connected a wire to somewhere I shouldn't have, and then all the onboard LEDs switched off and the Arduino Nano (clone) was cut off from the serial monitor. However, there as no smoke - the USB power diode was intact and did not give off smoke or look damaged.
Right now, the COM port doesn't show up when I plug it into the PC. Neither does the board power up from USB power. HOWEVER, if I power it using an external power source, the COM port shows up and the serial monitor works. When I remove the external power, it returns to not working. So data transfer from board to PC is ok, but not PC-to-board power. I have uninstalled and reinstalled the CH340 drivers, still dependent on external power supply.
I remember doing this before, but somehow it worked out. I remember that last time, I also fiddled around the drivers. My board uses CH340G - is this something to do with it?