I can't launch Arduino 1.8.4. It seems to be a font size issue :
In AppData/Romaing/Arduino15/preferences.txt, the font size is set to 12 which is >0 so I don't understand.
(It works with Arduino 1.6.1)
Any idea ?
The location of preferences.txt is different since Arduino IDE 1.6.6: AppData/Local/Arduino15/preferences.txt
Do you know how the font size might have gotten set too low? There was a keyboard/mouse shortcut (ctrl+mouse wheel) added in 1.8.4 to change the size and they didn't restrict it from setting the font to <1. That has now been fixed but the fix is only available in the hourly build or the next release.
I don't know, in fact, I wasn't on my computer when Arduino 1.8.4 crashed for the first time.
Indeed, before the software crashed, the person on my computer told me that the the font size has changed, so I think he has done this keyboard shortcut.
I changed the font size in AppData/Local/Arduino15/preferences.txt (it was set to -397) and It works !
Thank you pert :)