Cannot access dashboard

hi,
i have a problem to access my dashboard , i tried to reset password via myphpadmin and it didnt work. when i click on lost your password in the login screen it doesnt accept my username/email

i did restore db from backup and it didnt work.
the site is up and running.

it seems that the problem started when i install new wordpress site on the server. i was able to login to ne site it was fine and then suddenly i was not able to login to my new site or another one.

Any ideas?
thanks in advance