Buffalo 1T external hard drive won't start

Well bumping the drive would not cause damage. Most hard drives auto park. That means there is a small spring that when the drive is not powered it pulls the heads into the park position and off the media.
I suspect two things.
1. Bad drive. It happens, I have had a hard drive I purchased two months ago go bad on me so I went to Western Digital for a replacement under warranty.
2. Bad power. Check the power adapter. Did you use the one that came with the drive? If it is the one that came with the drive did you try plugging it into the wall to get "clean" power. If the drive is still under warranty tell them and they will ship you a new power adapter. If it is not under warranty. Bring it to Radio Shack so they can get you a replacement (Keep the reciept).
But if this was my drive and the data was CRITICAL I would pop open the drive take the hard drive out and get another external case for it.
Hope this is helpful.

I hate to be the bearer of bad news but your hard drive is most probably dead. What you can try is to put it in a level position (if it is not already). This is sometimes the cause of the problem , but other than that , there is not much that you can do.

The clicking sound you hear is the reading head that is jerking over the platter (hard disk) and thus , it is not reading any information. This sound is often affectionately known as the click of death and it normally lives up to its name.

As for recovering the data , It is a very complicated and expensive undertaking depending on how damaged the disc is. if the platter got damaged , there is no hope for recovering any damage.

DO NOT try and use the disc if you want the data recovered as it becomes more damaged every time it is running.

The cause of this problem is most probably that it took a bump or knock of some kind , but sometimes just happens with no warning or apparent reason.

I would take it to a repair/recovery center for an hands on evaluation, but you will definitely need a new hard drive.

Hope that this answers is helpful to you even though it does not do much in solving the problem.