Login to WP admin impossible

Hi
I cannot enter into the WP Admin tool anymore. I type the correct user name and password and after a couple of seconds, the browser stops searching and asks for the user name and password again. No error msg, no “incorrect password or username”. Nothing… Tried to delete cookies and browsing history, tried another computer, no success.
The FTP server is accessible, the site itself is accessible, but impossible to edit content.
THoughts?
Thx for your help
Bertrand