I had to download the trial version of WinRAR and then it did the trick; it recovered my 3000 files. However, all the files are kept in the WinRAR folder; I can't copy anyone of them to another location - then they disappear again. If I open the files one by one, I can save them in another location without losing sight of them (but 3000??). I don't mind to keep them in the WinRAR folder, but what will happen if the trial period expires?
Thanks a lot anyway for getting me out of trouble.