After having what Windows called "trust issues" when I tried to sign into a domain, I got OFF the domain by joining a workgroup with the same name as the domain.

Now that I'm off the domain and in the workgroup, I can't get back onto the domain at all:

"A duplicate (potentially the shorter NETBIOS) name exists on the network."

Then,

"An Active Directory Domain Controller for the domain *** could not be contacted."

I have administrative privileges both on the domain and the workgroup, so I'm not sure what the problem is.

Do you have a machine account on the domain already?

If you do , delete that on the DC, wait a few hours, then try rejoining.