plain password form in wp-admin

i got his problem when i try to log in onto my myadmin, please see the screenshot: https://snap.ashampoo.com/8AvfS4cx
also, the 404 page is replaced with that password form, here`s the screenshot: https://snap.ashampoo.com/dx3nCwIy

i`ll be very happy if anyone can inform me the reason why (probably hacked) and help me to solve this problem,,,,

thank you … ??