My external hard drive's... broked

[Masaki-kun]

So for my birthday I get an external hard drive (4/15). My computer's been literally full and hey, here's a terabyte of free space, so I start transferring my stuff. So Saturday (4/18) I put the disk in my backpack, get on the metro and ride it out to Virginia to my friend's house. I plug it into her labtop, which unlike mine is running Vista, and we work on some files I have saved to it (important ones) I tripped over the stupid power cable a couple times and about halfway though it stopped registering on her computer. I didn't think too much of it, and we didn't have time to restart the computer and try again (I barely made it back to Silver Spring in time to get home. Why doesn't anyone I know live in state?). So today I plug it in and it's claiming it needs reformatting. What's wrong?

The packing it up and carrying it?
The unplugging it a lot and knocking it over?
Some weird Vista thing?

And what can I do to get the data off it? (like all of my personal stuff. Almost all of it.)