1)Specfy the domain with the DNS NAME
2)If that doesn't work do an nslookup and look for the domain you want to join
nslookup
> mydomain.com
3)If that fails make sure the DC Is available , try and ping it with address first / then name
4)Make Sure your DNS Servers Are Specified correctly in the TCP / IP Properties of your adapter !
4)If the ping lookup fails by name do an ipconfig /release , ipconfig /renew + ipconfig /flushdns + ipconfig /registerdns
5)
5)Make sure FSMO roles are working properly around the domain . You can find out using NSLOOKUP , AD Sites and Services , ntdsutil
PS you can add the PC's Remotely if you want to , extract the x:\support\tools\support.cab to a dir and then go to CMD Line
dir>netdom join x.x.x.x /DOMAIN:mydomain.com /userd

omainadminaccount /paswordd

omainadminpassword /usero:localpcadminaccountname /passwordo:localpcadminpassword /reboot