Break seized

Check the rotor or drum for scoring, dimples, or dents. check the brake fluid to see if you need to change it and flush the break line. Check the pads or shoes to see if they wear normally. Check the cylinder wall to see if there is any scratch or wear. See if there is leak of break fluid around the cylinder or not. If it is 4 WD, it could be transmission problem as well. Above all, the more serious the symptom, the easier to pin point the problem.