jack the car up at the back with the hand brake on,try & turn the wheels by hand to see if it's both side's that's turning, if it's only one try checking the sliders are moving & that the pad's can move in the caliper, also get a mate to pull the handbrake on & off while you check the caliper where the handbrake cable loops on to it, see if it moves, if this does move try pushing it a bit with a screwdriver to see if it will go any further & stop the wheel from turning, also get your mate to press the foot brake & see if the wheel stops, if it doesent stop it's time for a new caliper