I added a computer to our small domain and ever since We cannot access our exchange server mailboxes.
It gives us the disconnected error.
Thanks for any help regarding this matter.

It's an IP conflict with your exchange server.

So many reasons in addition to IP address conflict. Please provide more information regarding your setup:

Type of domain, OS of servers, location of DNS, WINS, DHCP and scope of DHCP, server addreses including Exchange.