Establish a Trust Between the Domains
We will assume that you have already done this, but just in case this has not been done, please follow this YouTube video.
https://www.youtube.com/watch?v=t6VI6Xe3lck
(Please note we are not responsible for external content)
Test Logon to the Other Domain.
If the PC has already been joined to the original domain but does not yet have our Windows Logon client software installed*, please test that you can log on as a user of the other domain by logging in using a Down Level domain name format, e.g. otherdomain\username
If you get an error at this stage then you will need to put the PC back into WORKGROUP mode and then join the domain again.
*If the PC already has our client software installed then please log on as local admin and uninstall the software prior to testing as above.