Hey there, Logan!
You'd need to use a Mac to reformat your WD My Passport in a file system that can be read by Windows.
The Mac is needed to store your files from the external HDD until you've reformatted it for use with Windows OS, because this change will result in erasing all the data on the drive.
To avoid such future incidents, I recommend using the FAT32 file system because this format can be read and written to by both operating systems. Here's a tutorial that explains how to perform this:
http://products.wdc.com/support/kb.ashx?id=YvJkWM
Hope this helps! Good luck!

SuperSoph_WD