Ok, guys, finally an update on this.
Sorry it took me so long to open up my PC and look at the connections.
I think I figured out what's wrong here:
I noticed on my motherboard there are two different kinds of SATA ports, one kind is red (there is a total of six of these) and then there are two orange SATA ports and in the manual of my motherboard it says the orange ones are mean t for hard discs and can be used to configure RAID.
The DVD rom drive that does not seem to work is connected to one of these orange SATA ports.
I do have two discs in RAID 1 and according to the manual of my motherboard these discs should be connected to these orange SATA ports, which in my case they currently are not.
My question to you guys: how do I fix this? My RAID 1 setup seems to be fine, but if these two SATA ports are meant for RAID, I think I should hook up my two RAID 1 discs to them. And then connect my 3rd DVD rom drive to one of the freed regular (red-colored) SATA ports?
BUT: could swapping the ports my drives are connected to mess up my RAID 1 set up or mess up anything else on my PC? And I mean swapping from a red port to an orange colored one.
I'm hesitant to try this, because I am cared I could screw things up .....