Students who purchased MacBooks in 2011 or 2012 might want to seriously consider backing up all their files. According to the good folks at Helpline, these models appear to have a very high hard drive failure rate. I personally know three people whose hard drives have crashed in recent months, and there are many others with horror stories to tell.
If you think your hard drive has malfunctioned, double check by restarting your computer. Signs of a hard drive failure can include seeing a folder encasing a question mark upon starting back up.