Hmm, probably the driver supplied by Microsoft called "USB mass storage device" has been corrupted.
Re-installing it is a heart stopping procedure as it could end up disabling all your USB ports.
Basically in "Device Manager" you delete the device, then re-boot the system (use a full power-down & power-up) and let it find it again. Unplug any USB external devices during the re-boot. As you plug in each external device it should find and re-install the appropriate driver.
You can first try deleting only "USB Mass storage Device" and see if the automatic re-install fixes the problem, but if it doesn't you can then try deleting ALL the "Universal Serial Bus Controllers" and let them re-install themselves.
If you don't know what I'm talking about, don't try Take it to someone who does know what I'm saying. If it goes wrong, you could be into hours of time saving all your docs, data, emails and settings and re-installing the whole system from scratch.
In fact you should best do a (backup) save of all your docs, data, emails and settings before you start.