Windows 7 - Two drives, two OSes, only one boot

Hi, sorry if this has already been talked but I just couldn't find an answer, and sorry if this is not the correct place to ask.

I have a Dell Inspiron 14R (N4010), I bought a Sammsung SSD and installed it. Then I made a fresh install of Windows 7 in it. Then I replaced the Optical Disk Drive with an adaptor with my old HDD in it.

The thing is, I have the two drives with two different OSes, but my BIOS only detects the Samsung SSD to boot from, the Hitachi drive detects it as an ODD and I can't boot from it, is there anything I can to boot from that drive?

Have you tried looking at your SATA/IDE settings in the BIOS? They should be easy to understand as you are trying to get the same settings as your SSD for the Hitachi drive.

Well, I looked but I couldn't find anything like "SATA/IDE settings" in the BIOS as you said

This looks like a laptop. The SSD you should run in AHCI mode. But I am hot sure what that will do to the converted optical drive attachment.

You are probably better off if you put your optical drive back in and run your old HDD from a PCI eSata Express card using an external eSata enclosure.

Yes I know, I could just run the old Hitachi HDD from a usb port, but I just don't want to go everywhere with an extra hard drive, that's why I bought the adapter.

But as I said, the problem is that the BIOS won't detect the HDD as a bootable device/drive

Have you tried unplugging your SSD and only having your HDD connected to see if the problem persist?

Nevermind, I solved the problem, it was the boot order.
It only said Hard Drive, USB, CD-ROM, Network..... But I found by accident that I could expand the Hard Drive options, and there were both drives XD

Thanks very much to everyone!

I need some help doing this exact conversion. Mathius, can you link me the resources you used? Also, what adaptor did you use? Thanks!

Does anyone have any advice or links that would help? I just bought a Crucial M4 that is sitting on my shelf