I had a Firewall enhancement called 'Tinywall' installed on my computer so having seen your last message I thought that might be the problem although it should not be since I had the Arduino IDE on the list of programs that Tinywall allows to get access past the firewall. So, just to be sure |I uninstalled Tinywall using the uninstaller from the settings menu and Arduino IDE still would not start so I dont think Tinywall was the problem.
I then tried turning off Microsoft Defender Firewall from the Settings menu, ignoring the warning messages, but Arduino IDE still would not start. I then turned Microsoft Defender Firewall back on and I think it was at that stage that I got a dialogue asking whether I wanted to allow something, sorry I did not get a screenshot and I dont seem to be able to reproduce this. I clicked on the allow box and then Arduino IDE started normally and displayed my most recent sketch.
I do wonder if it might be possible for the Arduino IDE to display some message about there being an internet connection/firewall problem rather than just a blank screen with the Arduino logo expanding and contracting?
If I get this problem again I suppose my first action should be to turn the Windows Defender Firewall off and on again.
Thank you very much for your very prompt and useful help with this matter!
John