Windows 7 does not detect USB mass storage devices anymore

In an attempt to get a WD USB HDD to work I followed a suggestion to uninstall all devices of type Mass Storage using USBDeview. Now, Windows 7 does not show any mass storage device, even the ones that worked previously. For example, a connected USB pen drive is listed in USBDeview as not connected:

In the Device Manager it appears with an exclamation mark:

It is not shown at all in Disk Managment.

I already tried reinstalling my ThinkPad T420si's Intel chipset drivers, but to
no avail.

How do I get USB mass storage to work again?

Answer

Someone pointed me to a post in sevenforums.com by Difusal.
After following the steps in the post, I deleted the entry with the exclamation
mark in the Device Manager, then replugged the device. The mass storage driver
installed automatically, and the drive is now detected.

Steps, copied from the aforementioned forum post, reformatted and with typos
and spelling corrected:

1. Open Windows Explorer.




2. Go to C:\Windows\System32\DriverStore.

   
   

   You will have a couple of folders and files.

   
   

   You will have *.dat files and another file named: infcache.1




3. Right click every file (don't touch the folders!) and choose properties.




4. Go to the Security tab.




5. Click Edit.




6. Choose your account and check the box: Full Control (see ss)




7. Click OK.




8. Repeat for every file.




9. Select all the files (*.dat and infcache.1).




10. Press Shift + Del.




11. Click OK.




12. Now, go to C:\Windows\System32\Driver Store\File Repository.




13. Search folders containing usbstor.inf.




14. Open it (if you have more than one, choose the most recent).




15. Copy usbstor.inf and usbstor.PNF.




16. Paste those two files to C:\Windows\inf.




17. Reboot your PC and voilà! :b