Nokia Asha 502 - RM-921 Flash File / Firmware Latest Version Download Link

Check Download Link Below on this page Nokia Asha 502 - RM-921 Latest Version. 
Before flash your device take backup your all of user data first then flash. 
try move your all of user data other device. after flash all data will be lost.
check your phone hardware problem if phone have any hardware problem fix it then flash.
if your device only show Nokia logo on screen after turn on it's mean