F3 button for concordance search suddenly does not work anymore

Hi all!

All of a sudden the F3 button does not work any more.
Yesterday things were still fine and today nothing happens when I try to launch concordance search via F3. It works though via right click on the text but with my >30.000 word document this might take me 10 years to complete it.... ;-)

Any idea what happened or how I could fix this?

Thanks in advance!

Kind regards

Tatjana