Help solve the problem with access

Hello. I am having a problem with remote access to my server. my site is on a dedicated server. the ubuntu version on my server is out of date (version16.04.1). I made a backup of the site and reinstalled the ubuntu version. After the work done, I restored my site to a new version of ubuntu, since the site was deleted during the reinstallation. Now I cannot log into my server via putty. When entering a username and password, a message is written to me ACCES DENIED. The site works, but there is no access to it through the terminal. How to solve the problem?

Contact your server support team, mate! They'd be able to help you fastest.