quicklook not working

tonydenson wrote:

Space bar no longer gives me a preview of files - I just get a dialogue offering me to open it in Preview. Any thoughts please ?

Did you try rebooting?

Did you try a Safeboot to clear cache files?

Use safe mode to isolate issues with your Mac - Apple Support

From the terminal.app

Reset Quick Look from terminal, copy & paste:

qlmanage -r

and reboot.

https://apple.stackexchange.com/questions/259504/quicklook-not-working

tonydenson wrote:

Thanks for the reply. Safeboot temporarily fixed it but the terminal command had no effect (I rebooted). I suspect it may be a 3rd party add on doing something. I've read about things like Dropbox interfering with Quicklook. I'll try to eliminate things

  To trouble shoot further you can:

  Try a SafeBoot https://support.apple.com/en-us/HT201262

  Takes noticeable longer to get to the login screen, does a 5-15 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache,  etc.  Login and test.

This test will tell you if third party interference; extensions etc are not loaded in safe boot mode. 

  Test issue in another user (or guest user) account  https://support.apple.com/en-us/HT204443

  This will tell you if it a universal issue or isolated to your user/admin account. 

You can reinstall the macOS on top of your existing macOS for a refreshed copy with no lose of user data:

Latest Mojave Recovery a bit different—

How to reinstall macOS from macOS Recovery: https://support.apple.com/en-us/HT204904