glory

I had two hard drives in my old PC and I took them out. I tried putting them in my new PC one at a time and I could only get one to work. When I put the other drive in, I cannot see it on "My Computer". I can see it on "Disk Management" and it says healthy and active. For some reason I cannot change the drive letter, it pny allows me to delete the partition. There is some files that I need on that hard drive so I do not want to delete the partition. Any suggestions?