Check propeller placement according to the User Manual. If the propellers are not placed in their designated spots, this will cause the drone to flip over, fly incorrectly, or not fly at all.
Make sure that there's no hair or thread or any other object preventing the propeller from turning. If so, ensure that the unit is completely removed and the unit is turned OFF. Recalibrate the drone afterwards.
Check if propellers are no longer spinning. If a propeller has stopped turning, pull propeller pin slightly up, to ease the pressure, as it may have become compressed. Reset gyros and calibrate.
If this does not solve the issue, please contact customer service.