Those all in one systems are not really possible to fix yourself. You're gonna have to contact samsung, see if you're still in warranty, and see if its worth it to fix it.
A janky workaround might be to borrow a cheap DVD player from a friend, and see if you can hook it up to the AUX, D-IN, or some other audio input on the back of the old broken home theater DVD device. This MIGHT allow you to get sound from the new DVD player through the old sound system. No promises though.
Does the drive sound healthy or does it make clicking,grinding,crunching,etc. noises
Alec, thanks for your response. The DVD drive does make a noise while it tries to read the DVD inserted, or that is what I presume it is doing. However a few seconds later an error message, @cannot read disc@ (or similar) appears, then the disc drawer opens.
The system is no longer under warranty (unfortunately only 12 months) and when I contacted Samsung (Australia), via live chat, they wouldn't/couldn't tell me what the problem/solution was, but to take it to an authorised repairer.