External Harddrive Format problem on Macbook

I own a macbook and a samsung harddrive. Recently, my harddrive got a virus so I needed to restore is back to its original settings and wipe everything off it. When I put data on the harddrive from my mac, it is fine, and when I plug the harddrive into a windows computer, the data is all there and it is fine - BUT when I plug the harddrive back into my mac again, all the data is missing. This keeps happening, and I have tried using different data, so it must be the harddrive. I need help, I am thinking it might be the format of my harddrive or something but I am not very tech savvy so I don't want to do any more damage. Any help would be appreciated, thanks in advance

How are you formatting the drive and what file system (NTFS, HFS, FAT32 etc) are you using?