DIAGNOSIS: This is usually a power supply or thermal trip issue. The most common cause is a blown internal thermal fuse that's designed to protect the unit from overheating.
FIX: First, check the absolute basics: make sure the outlet works with another device and that the cord is fully plugged into the dryer's handle. If it's still dead, the internal thermal fuse is likely blown. This isn't user-serviceable. Your only real fix is to contact Revlon customer support for a warranty replacement, since this is a known failure point on units that get very hot.
IF THAT DIDN'T WORK: If you're getting a faint light or a brief power-on before it shuts off, the motor or main PCB might have failed. The outcome is the same—you'll need to pursue a warranty claim or replacement.
HEADS UP: Don't try to open the unit yourself. It's not designed to be repaired and you'll void any remaining warranty. Also, avoid using it on the highest heat setting for extended periods on thick hair, as that's what typically pushes it past its thermal limits.