What is the reason why the laser tube does not emit light?

Laser beam is generated by applying a high-voltage DC power supply to excite the CO2 gas in a glass tube. That means, the intensity of laser light depends on energy level. No matter it is a laser engraving machine, laser cutting machine or laser marking machine, the possible reasons why the laser tube does not emit light are as follows:
1. No signal from control card of laser equipment for laser tube power supply, so there is no power for laser generation;
2. Faulty power supply, can not send power to laser tube;
3. Laser tube is damaged;