Failure to start up

One day I was just working on my computer. Then I shut it off. I tried turning it back on later and it didnt start up. It showed the finder with a flashing question mark. It happened about 4 months ago and had my HD and HD cable replaced. All was well until now. This is the second time and I am a college student. It was quite disappointing and a hassle considering all my work is computer stuff. Is there a way to get a replacement lap top or a way to fix this computer without having to send it in again? also a way to get back my lost files? i need help ASAP. i haev the AppleCare Plan as well. will they replace my laptop?

this might help...
http://docs.info.apple.com/article.html?artnum=58042

yea tried those....it didnt fix. this is could be the second hardware failure. how can the Lemon Law apply to this? can it? is there a way to replace it?

You may have to reinstall your OS(operating system). That happened to me it said OS ?. That means there was some failure and your OS won't work until you reinstall it. Another problem is if you put in a new hard drive. You just have to reboot to the hard drive you want if you're sure your OS is properly installed because it automatically boots to the master hard drive.

i tried reinstallin but its not reading m HD what so ever...its missin for some reason