There are a number of reasons to give your BlackBerry PlayBook a "factory" reset. Chief among them: preparing your BlackBerry for rooting, downgrading your OS, and fixing a bricked/nuked tablet. It's fairly obvious when your BlackBerry tablet has bricked. Is your BlackBerry Playbook continuously rebooting? Does the LED double-flash when turned off? Like flash flash pause? Can't use your BlackBerry tablet? Yep, it sounds like you've got yourself a bricked PlayBook. It's easy to fix.
Before beginning, I should note that this process will completely wipe all of the data from your PlayBook. If you're planning on downgrading the OS or rooting your PlayBook, you should first create a backup of your tablet's contents. Personally, I skip this step because none of the data on my device is irreplaceable. If your situation is otherwise, make sure you make a backup copy. Of course, if your PlayBook is bricked, I hope you already made backups, because there's no way to recover that data at this point. Sorry.
To reset your PlayBook, you'll need the latest version of BlackBerry Desktop Software, a micro USB cable, a computer, and - of course - your PlayBook. Start Desktop Software on your computer and turn off your PlayBook. Yes, turn it off. Use the USB cable to connect your PlayBook to the computer and wait. After a moment, you should get an error message saying Desktop Software cannot connect to your PlayBook.
Click the "Update" button that's in the middle of the other two buttons, follow the on-screen instructions, and wait. Desktop Software will take care of downloading the OS and installing it to your PlayBook. The process could take up to an hour; make sure you keep your PlayBook connected until told it is safe to disconnect. Once finished, you'll be required to choose languages, set the time, sign in with your BlackBerry ID, and make final updates to the operating system - just like you did when you first received your tablet. After you're done, you'll once again have a working BlackBerry PlayBook.