Mac doesn't work correctly

I actually do aks this for a friend, because it's her laptop.

Her laptop is about two years old, MacbookPro.
When she was doing something it suddenly switched off. Then she tried to start it again, but it needed about 5 minutes to get to where she has to tipe in her password.
That worked fine, but then when it was loading the desktop it wouldn't do anything anymore.

Does anyone know how this can happen or what could be the cause?
She's going to a mac shop anyway, but maybe some of you know what this is.

Thanks a lot,
octopustea

(I'm not english so please excuse me if I spell things wrong or something..)

She needs to boot from the CD that came with it and reinstal the OS.

OS issue, or maybe even a Hard Drive issue.

I would use the original disks that came with the computer and in Disk Utility, run a repair on the main hard drive, and while your at it also check the permissions.