A user receives the following error message when attempting to log into a server: Username or password is invalid. Which of the following should the administrator do FIRST to fix the problem?

Installing OS patches is a remediation step that should only be performed after a root cause is identified, not as the first response to a login error.

CompTIA's troubleshooting methodology prioritizes identifying the problem first, which includes asking about recent changes to the system. A recent change - such as a password policy update, account modification, or directory service reconfiguration - is the most likely cause of a sudden login failure and must be identified before any remediation is attempted.

Attempting to replicate the issue is a valid troubleshooting step, but it should follow information gathering about recent changes so the replication attempt is properly informed.

Restoring from backups is a last-resort action that is inappropriate before the problem scope has even been investigated.