Additional info.

I went into the properties for the instance and changed the login details to system account which was the domain admin that I'd named during the installtion.

The username error has gone away but now it seems to be looking to a non-existent path on a second drive in the server as shown below:

FCB::Open failed: Could not open file E:\sql12_main_t.obj.x86Release\sql\mkmastr\databases\mkmastr.proj\model.mdf for file number 1. OS error: 3(The system cannot find the path specified.).