The application "preview" is not open anymore

What worked for me was going into the Applications folder and duplicating the Preview application, then opening the duplicate.

Does Preview open at all? If not, go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Remove the following. You may not find them all.

Containers/com.apple.Preview

Preferences/com.apple.Preview.LSSharedFileList.plist

Preferences/com.apple.Preview.SandboxedPersistentURLs.LSSharedFileList.plist

Saved Application State/com.apple.Preview.savedState

Credit Linc Davis for this solution.

My wife's computer had this yesterday too! I discovered that there was a preview running, but it was unresponsive. Oddly, force quit did not work on it, and the computer would not restart. I force rebooted the MacBook by holding down the power key and that worked (of course). Preview is happy once again.

I just had this happen for the first time on 10.11.

A quick fix in my case was simply opening Applications > Utilities > Activity Monitor, highlight the "Preview" process and hit Alt+Cmd+Q to end it. After that, Preview was back to normal operation.

Try Utilities>Disk Utility>First Aid> Repair Disk permissions

Restart the computer and try again.

Love it when I do exactly what you suggested, delete this and that, restart - & bingo! Thanks a lot