problems with external hard drive

I have a Power Spec external hard drive. It's practically brand new and I'm already having problems with it. Whenever I try to transfer anything to it off my Mac or when I try to save anything to it, my computer freezes. When I try to import video directly to it off my camera, the video is scrambled, the picture freezes (even though the camera is still going) and it doesn't save any of it. Does anyone know what the problem is?

Does it work fine on say, a PC?

Yes, it works fine when I just use the PC.