I recently purchased a seagate external hard drive and i would like to use it with my mac and pc. I connected to my pc and added files to it. then when i connected it to my mac the files were able to be opened but when i went to add files to the hard drive from the mac it told me that the hard drive couldnt be modified so i formatted it for a mac and then when i went to look at the files on my Pc it didint recognize the hard drive. Any advice in how i can make it so i can use my hard drive between both my mac and pc and be able to add files from both my mac and pc and be able to open them on both?