Printing & Internet Sharing Freezing Up Computer

A friend was messing with my computer, trying to get his computer to pick up internet from mine. I'm not sure what he did, I wasn't aware that he was doing this. Previously I'd used Internet Sharing a lot, leaving it on most of the day. It has always worked just fine. Now, whenever I go to system prefs and click on the Sharing icon, the sharing panel comes up but then freezes up the computer and I get the pinwheel. Usually I have to manually shut down the computer; occasionally I can force quit the system prefs but then the entire computer is sluggish and takes minutes to do anything at all, and I still have to end up shutting it off manually, it won't even shut down normally except once. Also, same thing with trying to print; the entire computer freezes up, I can't print anything. What could the issue be? I have OSX 10.5.8, MBP, 4g ram. Everything was working fine until yesterday, I can only assume my friend did something that messed things up. Anyone else had this problem, and hopefully have a solution? Thanks, I would really appreciate it, I rely on the sharing quite a bit.