Hello you all,
After reading all your advizes, the last advize of blackbird71 on April the 30th solved my problem. Before I installed a new version of opera I also installed a new version of Zonelabs. One of the improved functions in Zonelabs is "Anti-Keylogger". After I disabled this function and restarted Opera, my problem was solved. I am able to use the keyboard of my laptop again. I am happy that I can use Opera. It's one of the finest browsers available.
Thank you all,