My passport is not showing up in my computer

Hi I have a mac at home and a pc at work. After I bought my passport ( 1 tb) I forst connected it to my mac and did a backup of the mac. Now I have come to work and I want to access soem of the files on the external drive from my PC ( Windows 7) However, the PC at work is not showing the external drive so I am unable to open any files. Please help!!!

if you backed them up, you should have a original copy, no?