Restart Studio, then check the settings for spell check in File -> Options.

Thanks for your reply. Unfortunately it did not help. I even rebooted my PC, but still the same.

What does your spellchecker setting say? Do you use Word as spellchecker?

Yes, Word. But I don't think it is a settings problem. I can press the Check Spelling key, it turns light blue, as it should, but it simply does not react.

Please check, if the integrated Hunspell would work instead of Word. This way we can check, where the problem is located.

New info: It seems to be related to my monitors. I installed a third monitor this morning and it seems that the pop-up window somehow gets "swallowed" by the third monitor. I did some trial and error with several Trados files and with one file a tiny corner of the spell check window appeared and I was able to pull it to the middle of the screen. But this only worked once. Now it is gone again. I understand it is not a Studio-related problem, but if you happen to have an idea how I can make the pop-up to show somewhere within the screen again that would greatly help. Closing all other programs does not help, the window is gone. Thanks.

New info: It seems to be related to my monitors. I installed a third monitor this morning and it seems that the pop-up window somehow gets "swallowed" by the third monitor. I did some trial and error with several Trados files and with one file a tiny corner of the spell check window appeared and I was able to pull it to the middle of the screen. But this only worked once. Now it is gone again. I understand it is not a Studio-related problem, but if you happen to have an idea how I can make the pop-up to show somewhere within the screen again that would greatly help. Closing all other programs does not help, the window is gone. Thanks.

Maybe one of the solutions brought by Google will help you: www.google.com/search

Thanks a lot. The first solution proposed by Google does not do the trick, but I found something else and will describe it here, in case others experience the same problem in future:

Problem: Spellcheck (F7) pop-up window does not open after pressing the spell check button/F7

If there is more than one monitor installed the pop-up window may have moved outside the visible area of the screen, thus F7 is actually working but is not visible.

Under Windows 10 press the Window button (the one with the flag) on your keyboard and press "P" at the same time. A window will open where you can determine on which monitor your windows are displayed. Select "PC only". This will make all screens move back to the main PC/laptop, including the little pop-up window. Now that the F7 pop-up window is on the main screen the spellcheck can be carried out. This has to be repeated every time a spellcheck is done (or until somebody posts a better solution).