You probably have stumbled upon this common problem: When logging into a Domain Computer with a Domain user, this error appears: The trust relationship between this workstation and the primary domain failed.
What does it mean? Well, it basically means that the Domain Computer cannot authenticate against Active Directory, because the Computer Account password on the workstation is not valid anymore (this can occur when using Sytem Restore or when restoring from a backup).
How do you solve this issue? Pretty easy. Just remove the computer from the Domain and re-join. That works, but there is a cleaner and faster solution with one line of PowerShell code:
Test-ComputerSecureChannel -Repair -Credential (Get-Credential)
You will need to enter domain user credentials that can create or modify computer accounts in the Active Directory Domain.
You can check if the password of the Domain computer changed by viewing the attribute pwLastSet in the Attribute Editor.