Quick look not working High Sierra 10.13.6 Macbook pro mid 2012

I installed a new hard drive and ran into some trouble (machine opened with blinking question mark). Restoring the OS worked eventually but the restored OS was Mountain Lion. After I had a working operating system, I installed High Sierra and the security updates. Now, the space bar doesn't offer a quick look at the contents of pdf files (or jpg, mov). And the icons for some apps look different (see image). Here's what I've tried: I reinstalled High Sierra. Then I tried booting in Safe Mode - problem exists there too. Then I tried re-indexing Spotlight via System Preferences, following instructions available in this forum. That didn't seem to work. Then I tried command lines in Terminal following guidance I have received before from BDAqua. After that, Activity Monitor showed mdworker using a lot of CPU but the problem still exists after over a week.

I know others have had this problem and it seems that sometimes this resolves itself? Is there anything else to try? Should I just wait longer? Thank you for any suggestions.