Like the title said, I just installed my sound card, and tried to boot up but now I can't see my SSD, it boots up from my other hard drive, what the hell has happened? I've double checked all cables, nothing wrong.
Well loose cable would be the first culprit. Try to use a different SATA port, and maybe a different SATA cable just to make sure the cable wasn't somehow damaged.
Worst case you static discharged on the SSD or something abnormal happened. Check and double check the obvious before jumping to conclusions.
So I looked further into the BIOS and found that the SSD was actually there, but it didn't show in the first section. So I managed to boot from the SSD anyways.