I did reinstall iTunes already twice, following the instructions to do a clean reinstall. I do not think it wille be feasible to go on with reinstalling.
About looking into iTunes setup.exe: I get the option between "repair" and "reinstall", but the repair button does not work.
Then I went to control panel and tried to do "repair" in the installed iTunes program. It started "repairing" but without any result according to the backup option of my iPad.
So my conclusion is: iTunes is a too complicated program for me to use, and I will stop further efforts to make it working. Another disappointment for me is that ebooks and pdf's are no longer supported, and ebooks and pdf's were the only thing I used it for on my laptop.
Many thanks for your help.