Diagnosis
Complete power failure. The thermal fuse on the motor or the main power switch has likely failed. This often follows an overheating event.
How to Fix It
First, check the obvious. Ensure the cord is fully unwound from the rewind mechanism. Plug the vacuum directly into a wall outlet, not a power strip. Press the power button firmly. Listen for any click from the switch.
If That Didn't Work
Inspect the power cord for damage, especially near the plug and where it enters the vacuum body. With the vacuum unplugged, try toggling the power button rapidly 10-15 times. A faulty switch can stick in the off position. If still dead, internal repair is required.
Heads Up
Do not attempt to disassemble the main motor housing. It contains capacitors that can hold a dangerous charge even when unplugged. This is a job for a qualified repair technician.