avrdude: stk500_recv(): programmer is not responding after all tries

Question

After months of good use, both my boards Mega 2560 and Uno became unavailable for uploading sketch or burning bootloader.

Sketch uses 444 bytes (1%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.
C:\[...]bin/avrdude -CC:[...]avrdude\6.3.0-arduino9/etc/avrdude.conf -v -patmega328p -cstk500v1 -PCOM5 -Uflash:w:C:\Users\GREGOR~1\AppData\Local\Temp\arduino_build_242793/BareMinimum.ino.hex:i 

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 "C:[...]\arduino\tools\avrdude\6.3.0-arduino9/etc/avrdude.conf"

         Using Port                    : COM5
         Using Programmer              : stk500v1
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x03
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x03

Facts :

• v1.6.20 of the boards
• v1.8.5 of the IDE
• Windows 8.1 64bits
• Programmer: "AVR ISP"
• Drivers are fine (the boards are well recognized)
• Serial monitor works
• I'm trying to upload the "Bare minimum" exemple sketch
• Nothing in pin 0 and 1, nothing at all is plugged actually
• Get Board info:
• Uno : VID 2A03
• Mega2560 : VID 2A03
• From instructions here, every instruction is "echoed back"

What i tried :

• https://forum.arduino.cc/index.php?topic=385160.0
• avrdude: stk500_recv(): programmer is not responding
• https://zestedesavoir.com/forums/sujet/5676/probleme-televersement-arduino
• All other programmers
• A few old versions of boards
• Resetting the boards a few times, during upload, before, after...

Nothing works. If you have any idea.....

Thank you all !

Answer 1

It eventually worked by using upload / ctrl+U (what I didn't try... smh) instead of upload using programmer / ctrl+shift+U.

So i know now where it comes from, though I don't know what's wrong with AVR ISP.