Go back to the power options. Whichever one is selected, click "change plan settings" then "change advanced power settings". click the plus next to hard disk and type never into the box. Try that and see if it works.
Mine was doing the same thing until Cromewell suggested looking at the power options lol.Haha, I swear I looked for something like that... Just found it. Hard drive shut off after 20 minutes of activity, was driving me nuts.
All fixed now! Thanks for the help guys. Sorry for that double post my internet has sucked really bad lately, and I wasn't sure if it even posted either one.