How Can I Fix My Eternal Hard Drive?

I placed in the hardware before downloading the software. And uploaded 30GB of files (music) to the hard drive. And disconnected it from the computer. And now when I want to add more to the hard drive, or even access what I stored on there I can't. The computer cannot read the hard drive, does not even acknowledge it's there. Not even if I change the USB cord, or the computer I use to read the information. How can I get my files back, or get the computer to recognize the hard drive again.

Make and Models Details:Comstar 250GB hard drive
co-hde2-250G
FTY:NR
GEMCHU3.5"/JT

freakluver
September 2007