Question Computer recognizes drive when plugged in externally but not internally


Dec 4, 2014
My Acer laptop no longer recognizes the internal 2.5" 2 TB Seagate HDD that has worked for the past year.
I had a 500 GB Hitachi scrapped from a previous computer that I inserted into the exact same Sata input and it read no problem. So I concluded I must have ruined the hard drive and ordered a replacement drive, a 1 TB Samsung Evo SSD. I also ordered an external SATA/USB 3.0 cord to test the original hard drive since it seemed weird it just didn't read all of a sudden.
Today I received both the SSD and SATA adaptor cable. All three drives; the 2 TB Seagate, the 500 GB Hitachi and the 1 TB Samsung are recognized when plugged in externally, but only the 500 GB HDD reads when plugged internally... What could this be?

*Device manager doesn't show driver for SSD unless plugged in externally. In BIOS it does not show up as a boot option. Updated BIOS too.
**Ok so in BIOS i changed boot setting to Legacy mode and now the SSD is visible in bios, but now after posting, computer can't locate bootable device. Going to toggle back to UEFI and see if this fixed issue.
***Upon booting in UEFI, lose the SSD again, so didn't fix my issue.

Appreciate any ideas.
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