I'm using a MacBook Pro and I decided to try using my WD Passport external HD wirelessly by connecting it to my Airport Extreme. I had previously used this external HD for storing things as well as for my Time Machine backups. I'm showing my ignorance here, but now there is a folder on the external HD called "MacBook Pro.sparsebundle" with a little red minus or do not enter symbol on the icon and when I go to run Time Machine it says, "Oldest backup: none," and "Latest backup: none." But I can plainly see the backup right there on the external HD. I'm sorry I ever tried this and all I want is to undo whatever I did so I can go back to using Time Machine normally. I just re-formatted this external HD and backed up, and then did a bunch of changes on my MBP.
I don't want to start again at zero if there are options for me to continue using the sparsebundle.