If your hard drive is seagate, then you may need to update the hardrive firmware.
A firmware issue has been identified that affects a small number of Seagate Barracuda 7200.11 hard drive models which may result in data becoming inaccessible after a power-off/on operation. The affected products are Barracuda 7200.11, Barracuda ES.2 SATA, and DiamondMax 22.
If your drive is one of the affected ones, you can get the update firmware here.