Hard drive detection?

[moviemaggot]

So I have an external hard drive. I use it as storage for my mac and pc. whenever I would need something I would hook it up to the desired computer. But all the sudden last week my hard drive wont be detected on my mac, so I tried the pc and it works just fine.
What is wrong?

Any help is appreciated.
Thanks

[moviemaggot]

*Bump* Please help