There easy to fix. I got one in a trade last week and spent 12 bux to fix it...lol I didnt add new fans, just put 12v to them instead of 5v.
Could also be a broken solder joint on the mother board. You could overheat the console to see if that fixes it. Take 2 cotton swabs and pull the cotton off the ends. Insert one into each fan, turn console on. Let it sit about 10 mins, turn off console, pull swabs and let cool about 20 mins. Now, turn it back to see of that fixed it. If not, it will have to be taken apart.