something was unplugged usb caable check
USB cable? Do you have a hard drive outside your case?
Hard drive is usually connected by SATA cable.
A Hard Drive could fail at any time. http://www.hdtune.com/
Download and install the free trial copy of HD Tune.
Run the program to test the health of the hard disk.
If it's a Seagate Hard disk download SeaTools
If it's a Western Digital hard disk download Data LifeGuard Diagnostics