More info here in this post as to why this was happening and sharing here for others that may come across a similar issue:
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Mark Webber wrote a nice little breakdown:
If you have an unmarried board but working drive you will get:
Disc can be inserted/ejected
If a disc is inserted the disc icon will just spin
An audio cd will eventually be detected but not able to be played
Black screen when trying to launch anything from the XMB
Can upgrade/downgrade firmware (it only checks a board is attached, not that it is married up)
If you have a dead/dodgy board/cable/drive you will get:
No way to load/eject a disc
No way to downgrade without a bypass firmware
Black screen when trying to launch anything from the XMB
If you have a married board, but dead laser you will get:
The ability to play/install homebrew
Can play anything installed on the HDD providing it does not require a disc to be inserted (discless booting)
Can upgrade/downgrade as normal per the guides