WordPress fix can’t login to admin

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can’t login to admin, by maximig

Hello, after automatic upgrade to 4.9.4 I can’t login to WordPress administration. When I open link http://www.ceckopraha.cz/wp-login.php, instead of usual login page a popup window is opened and asking for username and password. When I type username and password, and I’m sure, that I typed it correctly, I”m returned back to login once again.
I already tried following:
– remove all cache & history & etc.
– renamed active theme
Nothing work. Many thanks for your help

can’t login to admin