Cannot transfer Schema role to another Domain Controller

Some of these tips are just general AD health checks.

1. Run dcdiag on both domain controllers to ensure everything is clean.
2. Verify that the FSMO roles are where you assume they are. (KB234790)
3. Look through Active Directory Sites & Services and confirm that you only see the servers and sites you expect to be there.
4. Ensure that your migration target (dc2) is a global catalog server.
5. Look through DNS to ensure that both domain controllers are properly registered, and there are no extra records lying around, especially in _msdcs.
6. If you are handling DHCP with Windows Server, you should deauthorize the original server before demoting it with dcpromo.

Why do you want to turn dc1 off? If there is only a single domain controller in your domain and it fails, you'll have a big problem on your hands. Consider leaving dc1 running as backup.

This TechNet article goes into great detail about how to sieze the roles.

Don't panic, the domain can function with both if those roles offline for a fairly long amount of time. Don't rush the recovery process because you're nervous. I would promote a new DC first, so that you have two in your domain, then worry about seizing the roles.

In addition to the seizure of roles, you will also need to clean up the failed DC's metadata in AD. See this Technet article for that procedure as well. You can do this after the promotion of a replacement DC and the role seizure process, so it's OK to do this last. It's important, but not as critical as the other two procedures.