OK, so I have this finally working, I had to do a lot of digging. but finally fixed why it's wasn't showing correctly.
The site created on the platform install was fine, the issue was when i changed this to be my old database, and old website.
In the database is a table called PortalAlias. This had the name of the current hostname from the old server, which is going to be changed when it is migrated. I was creating the new host with that name, but DNN was looking for the old one, so not opening up the site correctly.
I guess if you are just recreating the site from one to another this wouldn't be an issue.
I have managed to upgrade from 7.2.2 to 7.4.1, however this is giving me some issues with screen redirects, which i need to deal with, and just for testing purposes i added an upgrade to 8 this has given me errors to do with solpart, which again I will need to work through when i do that correctly, but for now I have at least one upgrade done, with at least no errors, or issues at least opening the site afterwards.
Thank you for all the help with this, I know it was a struggle, at least for me, but I got it done in the end.