Active directory 100% cpu utilization

When I open Active Directory on the primary server, it takes more than 5 minutes to open.

At one point it came up almost instantly, but now it is slow.

When I watch the processes under the task manager, it will show MMC using 99% CPU.

We have increased both memory and added CPUs to the server and it makes no difference.

I am convinced that it is software related, but my research has bore no fruit.

 

long shot but if you haven't pointed the server at the DNS server on your domain (probably it's self) that can cause a very slow response in AD.
I can't see that would give 99% CPU usage though.