Lost all default files

OK, so I came on my mac, plugged in the ext. hard drive and it opened the ext hard drive (1tb) with all the default files. It then said “Using external hard drive as Time Machine” and when I reopened the ext hard drive it had its files. I opened one of the folders and it said destination does not exist so then i closed Finder and looked the ext hard drive and I couldn’t find it. I unplugged and replugged it and it said “The disk you inserted was not readable by this computer.” I did some research and apparently Time Machine deletes all files to use it as a time machine. I wasn’t even trying to use it as a time machine but okk… ANy fix of way to get the default files back onto the hard drive?
I am running OS X Sierra on a 2011 Model MacBook Pro

Hi there,

If you know the model of your unit, you should be able to go to the download section on the WD website and locate the software and the documentation that comes with he unit.