Connecting G-Tech External Hard Drive

I recently purchased a G-Tech external hard drive. It worked great for two days, but today when I turned it on, my Mac doesn't recognise it. It doesn't appear in Finder and I can't see it anywhere else. The drive appears to be working OK and the disks appear to spin up, but no sign of it on the Mac. Can anyone help? I have a lot of video on the drive and have spent a lot of hours editing it!

MacBook Pro 216GHz Intel Core Duo Mac OS X (10.4.8)