SMPS may not turn because of these reasons.
1. SMPS is not getting power supply.
2. SMPS is spoilt
3. SMPS is detecting a short in machine circuit and is auto Shutting.
Note: Checking SMPS input when machine is on is risky task. You can get electric shock with with fatal outcomes. So please do at your own responsibility.
1. SMPS is not getting power supply: Take a multimeter and check the power input to the SMPS. The input Voltage should be 220 Volts.
If the input is correct check the output.
Turn on the power switch and check the voltage. Voltage should be 220 Volts. It the SMPS is not getting input then power supply/Wiring should be checked.
2. SMPS is not outputting power: If input is correct check the SMPS Output by keeping multimeter probe at output.
Note: Take a picture of the wiring before removing wires so you will have reference while reconnecting wires.
Check the output of the SMPS
If SMPS is not outputting power even after getting input, then remove all the output wires and check.
After removing all wires check the output. If output is 24 Volts after removing output wires then wiring short is the issue. Or else SMPS is damaged. If SMPS is damaged replace or else you need to find the short in the machine.
Finding short in the machine.