Will Active Directory Allow You to Add Two Computers of the Same Name?

Solution 1:

No, computer names must be unique. When you added the second computer with the same name, windows changed the sid in the AD database that goes with that name making the first machine not able to talk to the domain.

To keep the first machine on the domain, you'd need to remove the second machine from the domain, then readd the first machine back to the domain. Then add the second machine to the domain under a second name.

To keep the second machine on the domain, take the first machine from the domain, rename it and add it back to the domain under the new name.

Solution 2:

The machine name is the same, but the SID changes when you add a new computer with the same name as the old one. The SID is what everything in AD is tied to, not the same. This effectively "bumps" the old machine out of AD, as the corresponding SID no longer exists.