Network Diagnostics won't close or force quit

You have been set on the wrong foot alltogether here.

You are talking Network Diagnostics that will not quit.

Since the restart in Safe Mode (starting while holding the Shift key) the DiskUtility First aid tab (you have ElCapitan) did not solve the issue there has to be something else that crashes the diagnostics app. BTW this was a good advice by D.Cohen. Appreciates posts were all wrong.

As long as this is not solved I propose to quit Diagnostics by opening Activity Monitor, click the first column to make it alphabetically organised, select WirelesDiagnostics, click the little x in the top line of AM and click "forcequit".

After that first do a restart and a SMC and PRAM reset:

Reset the System Management Controller (SMC) on your Mac - Apple Support

How to Reset NVRAM on your Mac - Apple Support

If the issue still exists we go further.

Lex

Hi there, I have already tried via Activity Monitor, which didn't work but I haven't done the SMC and PRAM reset, so I'll try that next. Thanks!.

Hi there, thank you for your ideas thus far - but I've reset the NVRAM and SMC and the computer still: a) won't quit Network Diagnostics and b) won't let me shut down via the main normal menu; I have to do a 'hard' shut-down every time now. Please do you have any more ideas?

Regards, Kate

Somewhere I read a hint that may have nothing to do with your issue, but is easy to try:

SystemPreferences->iCoud: uncheck iCloudDrive. then restart.

Articles are there it might help : https://www.tekrevue.com/tip/how-to-force-quit-mac-os-x/

Force an app to close on your Mac - Apple Support

Hi, thanks for this. Unfortunately, I have tried all of these measures. And now, even if I don't open Network Diagnostics, I can not ever get the computer to shut down via the menu; it freezes on a blank desktop with mouse pointer visible, and I have to hard-reboot by holding down the on button.

In case you have installed anti virus , or a third party software / app it should be removed . sometimes if applications are corrupted or not responding it is advised to do a fresh installation. but before doing the user must take back up of all data

Run an etrecheck list now, and post it.

I have the same problem and I have spent two days following this thread to try all suggested measures but still it is not working. I know why it freezes and does not shutdown because it is happening to me too --Finder App is not responding. I hope there is someone out there knowing what happened to ElCaptain...

I have also just started getting this issue - wifi on ipad is fine but internet hardwired or wi-fi is crippled on imac - starting in safe mode helps but only marginal. Not had time to do a full check over yet will try this evening and post any positive results.

I have had the same exact problem for weeks now. I am unable to restart or shutdown my computer normally. I now have a software update for El Capitan and no way to update as I can't restart!

Startup Issues - Resolve

Startup Issues - Resolve (2)

Startup Issues - Resolve (3)