domain computer, no access from DC

When i am logged into my DC as Administrator, im not able to
access the computer \\downstairs.. the DNS is correct, and i get
the same problem with an IP.. it says i dont have appropriate
permission.. or whatnot.. anyway.. then it also says at the
bottom of the message

The account is not authorised to log in from this station

this is the DC.. geesh.. no matter what user i am on the DC is
the same thing.. but from my regular computer.. it work just fine

i have kicked and joint the computer to and from the domain.. i
did have a diffrent domain name before this started..

anyway.. i have no idea.. and suggestions would be great