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The PRAM reset has nothing to do with a hard disk issue. The PRAM reset just resets the startup disk to factory settings, and OS X is still selected as the default volume to start from, so this didn't cause the problem.
However, the slowness you experienced tells you that something happened with the hard drive, and the worst you can do is to restart your Mac, because you don't know if Mac OS X will start up properly. In your case, your hard disk has died.
Now you have to look for a new hard drive for your MacBook Pro. Any 2'5" SATA hard drive should work. Have a look at OWC to look for hard disks > http://eshop.macsales.com/shop/hard-drives/2.5-Notebook/ Seagate and HGST drives have good reputation.
To reinstall Mac OS X after installing the hard disk, hold Command, Option (Alt) and R keys while your Mac is starting and use Disk Utility to format your hard disk in "Mac OS Extended (Journaled)" > http://pondini.org/OSX/**1.html Then, close Disk Utility and reinstall. If you have a Time Machine backup, choose the option to restore a Time Machine backup