I made a fresh install of El Capitan in a Late 2009 iMac and restored 4 user accounts with Migration Assistant. While the other 3 work normally, mine (!) does not show preview thumbnails in finder. I have tried everything (finder preferences, preview default app for images, delete com.apple.finder.plist, reset NVRAM and PRAM, reset permissions and ACLs, with no success... Any help would be valuable, thank you!