Hi All !
I had the same problem with my HDD, a 320GB Toshiba external (well, inside was a WesternDigital drive, as Toshiba only makes 2,5inch and 1,8inch drives). I spent 2 weeks trying to solve it and finally figured out:
The USB chip (manufactured by Cypress !) can fulfill multiple roles. What will do once it received power depends on a small PLA array (non-volatile memory). For some reasons, probably poor manufacturing process by the vendor of external HDD, the programing of the chip is not done properly and after a while will "forget" it's settings.
The good news is that we can reprogram that chip ourselves, and this is done so:
1. First an alternative driver is to be installed, that driver is necesary to put the chipset in programming mode.
2. A new programing is performed. This takes very short as there are only 255bytes
3. External drive is power cycled and voila, it works again.
My unit was still under warranty. The added bonus is that all your data is still intact and accesible.
Toshiba Netherlands sent me to the shop where I bought it and the shop immediatelly offered to give me a replacement. Unfortuantelly I could not accept it since I did not wanted to loose all data I had. I suspected all the time that I could gain access to data by removing the drive from inside the enclosure and directly connecting it to the ATA100 interface in my PC, but that would mean also renouncing to the rest of the warranty (10months). In the end, after almost 2 weeks of research I could repair it using the method above.
On short:
If your unit is still under warranty and you can dispose of the data inside, you can send it back.
If otherwise, you can write me to grieg45@yahoo.com for the utilities.