Why won't my external hard drive connect?

I’ve got a WD Smartware hard drive and all my iTunes music/movies/etc is on it . . . I’ve had it since December, and it’s worked perfectly, until now. I’ll plug it in, and it’ll light up, but the hard drive won’t show up on my computer.

I’d love to know how to fix it. . . or even whether or not it’s fixable. Or if there’s at least a way to get all my data off of it. ‘Cause that’s where everything is.