I'm hoping someone can help me. I did not really understand how time machine worked. I'd lost my 20,000+ pictures not too long ago. I was able to rebuild my iPhoto and I salvaged the photos. That prompted me to buy an external hard drive just for my pictures. I purchased the Seagate Backup Plus Slim 2TB. I was not able to get the SG dashboard to show my PC and read that I needed to have it work with time machine. Somewhere after about 3 hours trying to figure this out (obviously I'm not so technology literate) I replaced the time machine back up with my new drive rather than using it in addition to the Seagate. I've just learned, via youtube, that I did it all incorrectly now causing this problem for me. Now when I look for my factory installed time machine drive it says "Your Time Machine backup disk cannot be found." My question is can I reverse the mess I made? I suppose that I can back up the entire computer with the new Seagate but it defeats the purpose of why I bought it to begin with. Help please.