Are you taking about the model you have in your signature? PRS-300?
It looks like it has a
common Mini-USB connection. It's not a Sony special cable. It should fit everything having such format, like older photocameras, older portable 2.5" HDDs and stuff. I say older, as the new format is Micro-USB.
I also assume you have read the manual and noticed the troubleshooting section and the hints provided at the corresponding sections. A nice chapter to read is "Device lock" on page 61
Finally, I would like to know what "recognizing" means?
The computer shows no sign of a Sony gear, or the Reader does not indicate its connection to the host? Or both?