I am very new to all this, but have programmed in other languages using several IDEs. Last night when returning to a coding session, I noticed that the background of the sketch window had gone from white to gray. Then when I tried to continue editing the sketch, I found that I could not make any changes. At all. Clicking anywhere on the screen is futile; the cursor never appears. Text can be highlighted but not copied or pasted. In short, I can’t go on from here at all. What have I done?
:):). Then could you please possibly post a screenshot of the Arduino IDE here. I have never experienced something like this myself (barring minor glitches which one can get fixed by updating to a newer version). Could you please state then the version number of your IDE, what operating system you are using, etc. It would be helpful.