I have an old PC that I'm hoping to install Linux onto. I removed the HDD and installed it into my DELL PC so that I could format the HDD. Once I reinstalled the HDD back into the old PC, it is not recognized. Did I miss a step or something?
The BIOS has to recognize before anything else. Change the settings there. You should have an option in the bios something like "HDD Detection". Since I dont know your specifics I cant offer any more advice.