Well your console is in the 1 year warrenty period so a repair is free. I suggest you start here:
Learn how to get your Xbox product repaired
Are you sure the fan has stopped working? I know sometimes its hard to see the fan spinning becuase of the coloring and angle of the vent
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Also make sure the power supply is getting good ventilation as well.
If the AC adapter is overheating, It can cause many nasty problems to boot.
Is your console sitting on carpet, or something else blocking the vents?