Article: If your PS3 is frozen, you can perform a manual reset. You'll have to do this from the console itself, as your controllers are likely frozen as well. You'll hear three rapid beeps and your PS3 will turn itself off. Don't turn it on using the controller, as it may not detect the PS3. Your PS3 will likely attempt to check for errors on the disk. This may take a while, or it may complete in just a few moments.

What is a summary?
Press and hold the Power button on the PS3. Hold the Power button for about 30 seconds. Wait a few seconds, then press the Power button to turn it back on. Allow the system to check for errors.