I know this issue is super generic, and that many others have asked about it before, but I've tried everything listed so far and nothing seems to help.
I have an arduino board (a Sparkfun Redboard, AKA UNO) that's been working great for about 3 months.
However, in a recent bit of experimentation, I connected the board's reset to ground (to stop it from running) so I could use the board's UART->USB converter without any interference. I've done this before with no issues, and it worked great this time.
However, now that the wire has been removed, the board does not reset (lights do not blink like they normally would upon reset). The power LED is lit, it is recognized as a COM port, and the little loopback (RX connected to TX) trick works fine. But, when I try to upload a sketch, I get
avrdude: Version 6.3, compiled on Jan 17 2017 at 12:00:53 Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/ Copyright (c) 2007-2014 Joerg Wunsch System wide configuration file is "D:\Shared\Program Files\Arduino\hardware\tools\avr/etc/avrdude.conf" Using Port : COM4 Using Programmer : arduino Overriding Baud Rate : 115200 avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x8a [....] avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x8a avrdude done. Thank you. Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
The "resp=" is different every time I unplug and re-connect the board. This error occurs even when just uploading the "barebones" sketch.
System: Windows 10, Arduino 1.8.2
Any help would be appreciated!