external hard drive not showing after snow lepard system update

I have just updated the system in my old MacBook to the last system update possible for the laptop (snow leopard 10.6.8) and the external hard drive is no longer showing up even after unplugging and restarting my computer.

I am using My Passport EDGE hard drive (which has been formatted to work on my pc and mac "fat32").

Any ideas on how to resolve the problem? I don't have another backup for the hard drive. Thanks in advance!