click here See my post at the bottom of the page. That's what can sometimes happen if the power is cut suddenly before the hard-disks have parked the heads and powered down.
Try configuring the power button action to initiate a shutdown if it is not already set like this. You'll know if it isn't because you'll probably have to hold the button in and then the power cuts off.
R-click anywhere on the desktop, select properties, screensaver, power and advanced.