I have 3 domain controllers, 1. was the main 2008 R2, 2. 2012 R2 current main, 3. 2012 R2 as second. The 2. dc was promoted, etc to become the main, and is verified as the main, and the 1. old main was down graded. When I shut down the old main (1.) every computer loses connectivity to the domain. The old main (1) has now went bad and is disrupting AD services in the environment. I can't bring it back to life. How can I force computers to use the 2. and 3. domain controllers? How can dc 2 see itself as the main?
When you demoted the domain controller 1, did you verify that active directory had fully syncronised to domain controller 2?
When you get the DCdiag, you may find that your FSMO roles are on DC1.
You now need to seize those roles over to DC2.
Untill you have run DCDiag and tried to find where the issue is, we cannot give you specific advice for this issue.