When we have pc client that is a member of Domain Controller, and tried to connect Domain Controller, we have problem like :
"Windows can not connect to the domain, either the domain controller is down
or otherwise unavailable or because your computer account was not found".
How to solve this problem ???
First, check the DNS of PC Client, that it must same with Domain Controller, and test to ping Domain Controller. When we have replied it from DC, it means that there is no problem with network connection between DC and PC Client.
Login to server DC with Administrator, then check the computer name of the PC Client at Server, if the PC client's name was registered or not. If the PC is registered at server DC, try to rename it or change computer (pc client) directly.
To change computer name : Right Click at my computer
Choose Tab Computer Name
Type Computer Name (with new one)
After that, Restart the computer and try to Join Domain, with the existing computer name. That is way how to solve the problem.
Goodluck and try it.