|This happens when the USB controller chip is seen on the USB pen drive, but the flash memory chip has failed or is not readable. This is cause by fractures in the solder that connect the chip to the PCB. |
Some chips will have legs and some are BGA "ball grid array"
The only way to fix this is to take the PCB out of the shell, and re-solder the chip. If it is a BGA type chip, you may get lucky if you could put enough pressure on the chip and plug it into your computer to read the data. A USB extension cable is good for this.
If that doesn't work then you need to reflow the chip.
Hope this helps