Ps3 frozen. Can't turn it off.

[Wright]

Well, huh...I've been watching Cole MacGrath's back for a while now. I removed the disc. I pressed the Power button with all my force. It doesn't do anything. The Ps3 is frozen and I can't turn it off.

 

The Ps3 is not mine, by the way... so I need advise. What the hell can I do now?

 

EDIT: This is a slim Ps3. That means, no power switch at the back of the console.