I have a Seagate External Hard drive that I had some files and photo's saved on from my old PC.
I plugged it in and it would'nt let me save my iphoto library to it, so I thought perhaps it was not formatted for use with an imac, so I searched this site and made some changes and added a Partition 1, and straight away I was able to get Time Machine working and save my whole Mac onto my drive.
But now my concern is, have I lost my old files on my Seagate I can now move my iphoto library onto the Seagate no problem, did I reformat and lose everything? Can I get it back?
Recovering files from a Windows drive having been partitioned, formatted for HFS+ and then written to is highly unlikely. You may have some minor luck using a file recovery program like Disk Drill Pro, but it's doubtful.