SOLVED:
I solved it the issue. It was because that the disk lettering was already enumerated for the other partition on the initial installation. You couldn't change it in disk management since it was in use.
I opened the registry on disk d remotely.
I went into HKEY_LOCAL_MACHINE > SYSTEM >...
I have a single drive partitioned into 2.
I installed windows 8.1 onto partition C.
I cloned partition C onto partition D using EaseUS Backup.
I used easyBCD to add a boot entry for partition D.
I know if you do two separate installtions through the installer, windows makes the...