Level 2.... Bottom right hand corner, there is a small tile on the floor you use to fix the missing tile. I had trouble finding this myself.
I got stuck on level 3. Said that stupid vent was too high, did everything to make myself get up there... said its SCREWED SHUT, WTF!?! I dont have a screwdriver, so how do I open this! Clicked on everything, tried everything, nothing happened! A walkthrough would be nice. Whatever, you get 3 stars for that. =\