Well, the first guess is that your SI 3512 (which is a chip) is on an add-in card, and the add-in card is not working.
What kind of motherboard or prebuilt machine?
Is the SI 3512 mounted on the motherboard, or on an controller card? If the latter, what model of controller card?
Are there other drives on this machine that are detected? What are they attached to?
Did any drive attached to the SI 3512 ever get detected, or is this a new situation that is not working as expected?
Have these drives ever worked on any machine, or are they new?
And it's always a good idea to re-seat the power and data cables, just to test.