not uploading

[vbee]

it used to upload, but now its not. help!  

[ieee488]

it used to upload, but now its not. help!  

so little information

[pert]

Please do this:

• File > Preferences > Show verbose output during: > compilation (uncheck) > upload (check) > OK
• Sketch > Upload
• After the upload fails you'll see a button on the right side of the orange bar "Copy error messages". Click that button.
• Paste the error messages in a reply here USING CODE TAGS (</> button on the toolbar).

[larryd]

Maybe you burned up the Arduino.
Maybe you are not following the upload sequence properly.
Maybe you have a bad cable.
Maybe you clobbered the bootloader.
Maybe you should try the loopback test.
Maybe you should try some troubleshooting.
https://www.arduino.cc/en/Guide/Troubleshooting#upload   

[vscelwan]

I change the crystal on board to 16MHz,

Change:
mega.menu.cpu.atmega2560.upload.protocol=wiring

To:
mega.menu.cpu.atmega2560.upload.protocol=stk500v2


After that Upload without issue

[pert]

@vscelwan, please stop posting this all over the forum. Maybe in your very strange circumstance that was the solution but for you to post those instructions on a thread where the only information we have is "it used to upload, but now its not" is extremely unhelpful.