When you "emptied the recycle bin" what you actually did was delete most of the binary programs from his computer. You have basically bricked him laptop... How you did that without it asking for a password and you not wondering "hmmmm, should I be deleting files I don't know if my friend may need again" is beyond me. But I regress.

Go ahead and turn it off, it will NOT boot again but leaving it on will not help at all as there are no programs you can run that will allow you to do anything useful. What you will need to do is use a liveCD such as Ubuntu Resuce Remix which can be found here.

You could also use a normal Ubuntu liveCD as well but the rescue CD may make it a little easier. You will need some CDs , DVDs or a usb drive to put the files on while you re-install the OS and then you can restore his files. Or if he has another partition you could move all of the files there while you restore the OS. I would highly recommend you tell him what you did and get his help before you make it any worse and just flat out delete all of his data.

Good Luck!