I'm totally new to this forum and I'm probably doing this all wrong. Forgive me. I recently purchased a IMac. I was using a PC and had an external hard drive (Seagate) where I stored all of my important files in preparation for the move. When I put up my Mac, the computer read the external drive and I was able to see the files. I opened up an old PC file on the Mac and updated it and put it back on the hard drive. Since then, the computer doesn't read the drive. When I plug it into my PC, it asks me to format it. The Mac doesn't recognize it. Is there any help for this?