Diagnosis
This is almost always a power supply issue. The heater's internal fuse has likely blown, or the power cord/connection has failed.
How to Fix It
Unplug it, wait 5 minutes, then plug it directly into a wall outlet. Don't use an extension cord or power strip. If still dead, check your home's circuit breaker or GFCI outlet first. If those are fine, the heater's internal thermal fuse (a small safety component) is the probable culprit. This isn't user-serviceable—it means the unit needs replacement.
If That Didn't Work
The power cord itself can fail where it bends near the plug or enters the unit. Inspect for any kinks, cuts, or discoloration. A damaged cord is a fire hazard; don't use the heater.
Heads Up
These heaters lack a user-resettable button. If the internal safety fuse trips, it's a permanent lockout. Contact Amazon for warranty support if it's new.