Welcome to the TH Community, @pmoa_cthulu!
This sounds pretty unfortunate, indeed.
I'd advise you to completely unplug the HDD from the PC and then attempt to boot into the SSD again. If the issue is still present, I'd suggest you try to boot into the Advanced StartUp Repair options from your Windows installation media. This will hopefully help you resolve the boot up issue with the SSD. If the problem is still present, power down the system and reseat all the connections inside, making sure there's nothing loose. It might also be a good idea to
reset BIOS, just make sure you re-configure all the manual changes you have made in the BIOS interface again because they will all go back to their factory default condition.
As for the hard drive, I'd strongly recommend you try using a different SATA cable and another PC (if you have access to one) to check how it will get recognized there. If the other computer is facing issues with the Start up processes as well, then you are most probably dealing with a failed hard drive. Another alternative to troubleshoot it would be to connect it externally via a docking station/external enclosure with an AC adapter and test it for any sort of defects. You should be able to do that using
the HDD brand-specific diagnostic tool or a third-party alternative. Check what the health and SMART attributes will show about the drive.
Keep us posted & good luck!
SuperSoph_WD