wp-admin 404 error when logging in

Today when I logged in, I got an 404 error for the wp-admin page.

I´m still logged in, I can go to certain sites like 'wp-admin/options.php' If I enter it in the url, but when trying to access other menu items, I get a 404 error. I haven´t done any updates for 2 weeks, and the sites have been running nicely, til now. How could this have happened? Anyone else had this kind of issue?