Help

My MacBook was running really slow. I only had two applications open firefox and iTunes. I got frustrated with Itunes because it was running slow so I tried restart my MacBook. I turned it off and now it won't boot up. It either gets stuck on the apple screen with the spin wheel or only the white screen. I tried booting up in safe mode, didn't work. I don't have any instalation disks or anything like that. I thought maybe it over heated because it was about 100 in my house and I was charging the computer while using it. But I let it cool down and that didn't work. Also it was at around 30% batery at the time of the problem. Now it needs the power chord to turn on. A folder with a question mark started popping up after I let the computer run on the white screen for a while.