shower knob has no resistance *video*

[noknowledge]

one day i went to turn the knob just turn the water on and it just spins freely with no resistance. i wanted to take it off to see if i could fix it but can't figure out how to take it apart. their are 2 small phillips heads but they are not very accessable because of the knob. any idea what would cause this or how to get it apart. just incase it matters the brand is Moen.
you can watch this short clip to see what i'm talking about.

Click here to watch shower-33

[jsouthco]

On the face of the knob, use a flat blade screwdriver to remove the cover. You will find a phillips head underneath that attaches the knob to the end of the stem.