I know after Windows XP release Universal USB Storage Driver is not an issue for any USB. Two days back, I was facing USB detection issue. My Computer was not recognizing my portable hard disk either. Finally on Sunday, I got two hours to fix critical problem and share my findings with you with solution. I am share my findings based on Microsoft Windows 7 only.
"USBSTOR.sys" file is USB Mass Storage Driver for detect USB Mass Storage Device(s). You can find it in folder location "C:\Windows\System32\drivers". ‘.SYS’ files communicate with Operating System directly and guide Operating System what to do with device and how to do.
Operating System has one utility (so called, Driver Detection/New Hardware Found) for new device detection and registration for correct version of device driver to communicate with Operating System. Driver Detection utility needs INF and PNF file for device detection and registration for communication with hardware. You can find them in folder location, "C:\Windows\inf".
[Additional Information, INF file has all driver setup information and PNF file has some dependency and additional information of driver (in nontechnical words) (Technical team is Precompiled Setup Information).]
Some time USB Mass Storage Device has problems due to driver installation and un-installation frequently OR due to any possible bug of installer/setup. Installer can delete .INF, .PNF and/or .SYS file(s).
Windows 7 has almost every Device Driver backup in folder location, "C:\Windows\System32\DriverStore\FileRepository\". Go there and search folder "USBStor.inf_******" (* is driver identity number). It will have three files of USB Mass Storage Driver. Please follow instructions to restore them,
1. Copy "usbstor.inf" file and "usbstor.pnf" file, and place in location "C:\Windows\inf".
2. Copy "usbstor.sys" file and place in location "C:\Windows\System32\drivers".
3. Reboot Operating System.
4. Say AHO! After login. (Please note without AHO! USB will not work. A Joke)
5. Insert USB and use it.