Macbook Pro 13-inch stuck at Gray screen with apple logo and wheel
Well, seeing as the laptop is at least attempting to boot from the hard drive, I'd say that your hard drive is fine. 

My recommendation is that you reinstall Mac OS X. An early 2011 MacBook Pro would've come with Mac OS X 10.6 Snow Leopard, so you should have had some DVDs come with the MacBook Pro when you bought it. Use those to re-install Mac OS X 10.6.