I think you are confused somewhat...or I am (highly possible)
A SATA drive doesn't reflect as "slave" unless it is in the BIOS. I know that my BIOS reflects them that way, but I pay no attention to it because I don't boot from them.
If your BIOS is like my BIOS...it moves a SATA drive ahead of any PATA/IDE drives in the boot order listing in the BIOS...when SATA drives are attached. So, it is possible that attaching a SATA drive to a system...may unintentionally change the boot-order-option sequence as reflected in the BIOS.
It's also possible that your BIOS has your optical drive as the first boot device...I don't know, but some leave their systems that way.
In such case, the system would try to boot from a SATA optical drive (which, of course, can only be the boot device if a bootable disk is inserted) and the result would be a system that would not boot.
If this is the case, the solution is simply to make your boot drive your first boot option.
If I've not understood...just chalk it up to me being me