The trust relationship between this workstation and the primary domain failed" error when you log in to Windows 7

1. Use a local administrator account to log on to the computer. 
2. Select Start, press and hold (or right-click) Computer > Properties.
3. Select Change settings next to the computer name.
4. On the Computer Name tab, select Change.
5. Under the Member of heading, select Workgroup, type a workgroup name, and then select OK.
6. When you are prompted to restart the computer, select OK.
7. On the Computer Name tab, select Change again.
8. Under the Member of heading, select Domain, and then type the domain name.  
9. Select OK, and then type the credentials of the user who has permissions in the domain.
10. When you are prompted to restart the computer, select OK.
11. Restart the computer.