Cannot mount volume - External Hard Drive [Ubuntu 7.10 Gutsy Gibbon]

Okay, I'm new to Linux and I'm having problems getting onto my external hard drive. Before, I've been able to access it but now I'm getting the error message "Cannot mount volume".


http://img175.imageshack.us/img175/2849/62506110gd3.jpg

I can't access Windows at the moment due to other problems, but I'm guessing there's some sort of way to fix this without using Windows, right?

Any help is greatly appreciated!