unable to log in to dasboard

I used the simple settings but the main menu stopped working, giving 404 errors. I am using Polylang to make the site bilingual. The second menu, accessible with the language switcher, still works. After logging off I am not able to log in to the dashboard.
Any advise apart from doing the manual disinstallation?
I am not a developer, just a end user who manages his own website.
Alf