DIAGNOSIS Yeah, this one's common. The humming means power is getting to the brushroll motor, but something is physically preventing it from turning. Usually, it's hair or string wrapped super tight around the ends of the roller, jamming the bearings.
FIX Flip the vacuum over. You'll see a silver plate covering the brushroll. Use a coin to turn the two silver locks to the unlock position and lift off the plate. Pull the brushroll straight out. Use scissors or a seam ripper to cut and remove all the hair and debris wound around the ends of the roller, especially where the plastic bearing caps are. Clear any debris from inside the empty brushroll chamber too.
IF THAT DIDN'T WORK With the brushroll out, plug in the vacuum and briefly turn it on (in upright mode). If the small drive belt inside the chamber spins, then the brushroll itself might be damaged. If the belt doesn't move, the motor drive could be shot, which is a bigger repair.
HEADS UP Don't run the vacuum for more than a few seconds with the brushroll out—you'll just sling the drive belt off and cause a new problem.