Security issues after restore of Server 2008

Hi
I had to do a full restore of our local DC running Enterprise 2008 R2 today,
using windows server backup. The restore was straightforward and all
services start but the group policy is not updating and the DNS server
cannot be accessed - all pointing to a security issue following the restore.

I have found an article saying that the security details change following a
full system restore but it didnt explain how to recover the situation -

Can anyone tell me
a) is this correct?
b) whats the proecdure to resolve the situation?

Thanks
Roger.