Problem with Starting up Mac

Hi guys, this is my first post.

Im seeking some help regarding a Macbook Pro (13") that i was recently given as a present. I used to use PCs but then i found that using a Mac was comparatively better. I was having fun learning interesting things with my Mac, until...

I gave it to my little sister one day, for some homework (shes 8). When i got back, to my disbelief, the Mac wouldnt start up.

The Macbook would only load up the white screen, with the loading bar, the bar then reaches about half way, before starting again, only for it to reach half way again, and then suddenly turn off.

The only way i can do anything is on the windows that i dual booted on it, but its not very good.

Any help would be appreciated.

Note: merged and deleted crosspost. Please do not create duplicate threads here. We are not so big that your thread will not be seen.

Do you have the original install recovery disks that came with the MBP? If you do, boot the machine with install disk 1. (Leopard or Snow Leopard) Hold down the C key as soon as you hear the chime. Keep holding it until you see the Apple appear. It may take a while to boot from the DVD, so be patient.

After it boots to the install screen, click on the top menu item called "Utilities" and then select "Disk Utility". Highlight the hard drive on the left side and then select the First Aid tab on the right. Run the verify and repair function. Report back the results and we'll go from there. (The verify and repair will check your hard drive which may be having problems.)