Sounds like a power issue. The BIOS should at least recognize the drive is there, regardless of what is on the drive. You may want to make sure whatever you're plugging into is actually set to manage SATA drives in the proper mode.
Maybe think about getting a USB to SATA adapter for cheap to make sure.
Other things:
are you hearing the drives spin when you plug them in? (SAS probably needs 5v or 12v, it'll say on the drive)
did you check if there are jumpers set for a specific mode of operation?
are you positive your drive controller can read other SATA devices?
To your last point, of it's an 8x card, it should work fine in a 4x slot, just at 4x speeds.
Edit: does your motherboard not have SATA? Try it there instead of this card to rule it out as a problem.