Hard Drive problems

I have a WD passport SE that i used on my old VAIO that I want to use on my MAC. Ive downloaded Paragon NTFS, the first time I used it I was able to read and write on the hard drive. I let my buddy put some files on the hard drive from his computer and now my Mac will not recognize it nor will the Paragon program. Does anyone have any help on this situation. I want to keep the hard drive in NTFS format due to a lot of my military friends have windows OS pc's and we share a lot of files. Any help is appreciated.

You may never know exactly what happened, but try having one of your Windows buddies reformat the drive. You could also try different USB cable, but that's a long shot.