First, check if the vacuum is plugged in. The power cord is manual-wind. Ensure it's fully unwound from the cord wrap and the plug is secure in the outlet.
If power is confirmed, the issue is likely internal. The model NV356E has no user-serviceable power switch. Do not attempt to open the housing.
IF THAT DIDN'T WORK: The motor may have overheated and tripped the thermal protector. Unplug the vacuum completely and let it sit for 45-60 minutes to cool down. Then plug it back in and try again.
HEADS UP: If it still won't power on after a full cool-down with a confirmed working outlet, the motor or internal wiring is faulty. This requires professional service. Contact Shark support at 1-800-798-7398.