Usually after I open quicklook and then close it again I cannot open quicklook again. And if I right click on an icon it lists exit quick look as an option but when I click it nothing changes.
What's my problem here?
I am on OSX 10.11.6
Try the following:
qlmanage -rand hit enter
qlmanage -r cacheand hit enter
This should force QuickLook to reload the generator lists and reset the disk cache.
Pressing the function key and the spacebar fixed it for me.