Not much educated on the "question mark" subject, but its happend 2 times to me and one time in the office, when it happend with me i booted from CD, formatted the HD ( every computer i got till date, i partition it so i can use one section for a backup, it would be a good practice to do so) and it would work just fine again. The second time i got the " ? " i did a CD boot, ran diskutility and it showed errors with the main partition and showed sucessful for the 2nd partition, i tried to fix permission and repair, but it couldent, hence back to square one, i wiped that partition clean and installed the system again. Voila m back up on OS X.
I wouldent know if this would help you in anyway as you would have files on your hard drive you need. If you give it to a service center, then they blindly tell you you need a new HDD. but as magnus said you could try out diskwarrior etc and see if you can sort it out though that first. Hope that helps.
Cheers.