Okay, so to recap,
* Before, you use SATA power connection on HDDs & ODD, Segate HDD did not show up on BIOS. (Is that right or did you use molex to SATA adapter before?)
* You now use molex to SATA adapter on WD HDD & ODD while Seagate HDD is still on SATA power connection. BIOS did not pick up WD HDD.
Keep in mind that one downside of using molex to SATA adapter is that there won't be a +3.3 V rail (molex only provides +5 and +12 V, no +3.3V or orange wire). Few SATA device do use +3.3V, hence such adapter won't work.
Try to redo your wiring again and post by result.