I start up and get a screen with a picture of a file folder with a question mark on it.

This means that your computer cannot boot up fully because it cannot find the hard drive which it's system files are stored on. This can mean that your hard drive has failed. But, I know many people who've been able to restart after letting it sit for 30-45 minutes. If you are able to start it again after a period of time I strongly suggest backing up your files beacuse it is a real possibility that your mac could be in the beginning phase of hard drive failure.

http://support.apple.com/kb/PH11046

Use Startup Manager to select Startup disk.

http://support.apple.com/kb/HT1310

Repair Disk

Steps 2 through 8

http://support.apple.com/kb/PH5836

Reset PRAM.

http://support.apple.com/kb/PH4405

Best.