Hey there, Stylo.
Basically, what @boosted1g said is correct about faulty drives preventing healthy ones to work properly and causing issues for the whole system. However, if you manage to get the computer to recognized the drive, you shouldn't try to fix anything. Your first priority here is data recovery, so that's where you'll need to start. Since we don't know the nature of the issue, you shouldn't risk using it for tests or repairs of any sort as this could make things worse. So the best case scenario is to get the computer to boot and recover the files via data recovery software: https://www.lifewire.com/free-data-recovery-software-tools-2622893.
Before you give it a try with an external connection (which is again a good suggestion), you could try using Ubuntu Live USB, to see if that OS is capable of recognizing and accessing the drives partitions so that you can transfer your files to a healthy HDD.
Hope that helps. Please keep us posted.
Boogieman_WD