Was given a cheap chinese made cruiser bike a while ago and I am just putting it back together for my son to go posing on......but the rear sprocket is not locking and therefore will not turn the rear wheel. Is it likely to be a fixed gear or free wheel and will it be the locking ring (though doesn't really look like my sons flip flop on his fixie? Any help would be appreciated. guym
If it has more than one gear and/or has hand brakes, it is likely to be a freewheel.
If it does not have hand brakes, it is likely to be a "coaster brake" which is a single speed type but not a "fixed gear".
If a freewheel, you probably need a new freewheel.
If a coaster, it could be a problem inside the hub. But more likely, the chainring just slipped off the place it attaches to the hub with a snap ring. Google coaster brake diagram for some pictures.