My computer wont recognize my "My Book"

Yesterday, when I was moving my computer a meter or two, I forgot that the external hardwire was plugged in. And it fell a little bit, but it did stand on the ground and did not get any marks on the outside. It worked perfectly after the fall, but today my computer wont find it. so please, can someone help me?? :slight_smile:

Its a windows xp :wink: