There is a small bug with Arduino IDE 1.8.4. A keyboard shortcut was added in this version that allows you to change the editor font size via ctrl+mouse wheel. Unfortunately the code doesn't prevent you from shrinking the font size all the way down to 0 or a negative number. If you exit the Arduino IDE with the font set to 0 or less you will not be able to start it again, you just get the splash screen and then nothing. If you check the console output during process (arduino_debug.exe for Windows users) you will see the error:
java.lang.IllegalArgumentException: Font size must be > 0
If this happens you can fix it by:
- Open preferences.txt in a text editor.
- Change the number at the end of the editor.font property setting to something greater than 0.
- Save the file.
OR:
- Download the hourly build: http://www.arduino.cc/en/Main/Software#hourly
- Run the hourly build (the bug has been fixed in the hourly so it will start).
- Use ctrl+mouse wheel to change the font size to a size greater than 0.
- File > Quit
- You can now remove the hourly build and go back to using 1.8.4 again.
I'm not sure what possesses people to shrink the font size down to invisibility but it's been reported quite frequently since the release of 1.8.4 so I thought it worth adding a note to this thread.
Please DO NOT report this on the GitHub issue tracker. The bug has already been fixed and the issue has been reported about 7 times again since the fix. Arduino IDE not working when accidentally I reduced the font size to very small · Issue #6689 · arduino/Arduino · GitHub