It sounds like your drive died, or the board on the enclosure died.
Take the HDD out the enclosure and put it in your PC hardwired and see if you can access it.
If the drive works, then the board in your enclosure prolly blew a something.
If you don't have a PC, then you will need another enclosure or one these:
http://www.newegg.com/Product/Product.aspx?Item=N82E16812232002
I love this little adapter. It lets you hook up any type of drive externally to a usb.
I bought mine so I could hook up an old 5.25" dvd-rom from an old tower of mine to the work netbook so we could watch movies at work.
My boss thought he was so slick buying netbooks so we couldn't watch movies, LULZ!
I also use it to backup my pc onto a spare hdd I have in the closet, and I used it to clone my laptops HDD to an SSD.
*NOTE:
ALWAYS plug the power adapter into the wall first, then plug the adapter into the drive, then turn on the power switch on the adapter.
If you do it in any other order you risk frying your drive from a power spike.
This is good advice for any device that has a transformer on the power side.
I know a thing or 2 about HDD's, here are my credentials

:
That is the media PC.