Windows Server 2003 R2

Problem:
Windows Server 2003 R2, server keeps locking out Remote Desctop Users. If I change the DNS numbers around i.e. Prefered to Alternate and visa versa, the sever can then get on the internet, Remote Desktop users can log on, and you can ping the server IP. The next day the same thing happens Remote users can gett on, cna;t ping, can’t browse internet. Change the prefered and alternate DNS server around and all works again until the next day and the same again. Can’t find why this is happening. HELP!!!!!
Kevin