sony vaio ext hard drive

Hey i was hoping someone could help. I bought a Sony Vaio External Hard drive about 6 months ago, and after using it fine for about 2 weeks and storing lots of things on it, it stopped working. It connects via usb to mini usb, then when plugged in, it registers with the computer that it recognises the hardware, then when trying to open it, it doesn't work. It didn't cost me a lot of money, but i was speaking to a friend the other day who spent a lot more, who has a different one (not Sony) and has the same problem. Anyone know of how to fix this???!!! Chops