Make sure gen isnt stopt on protection overtemperature or oil level or coolant level. try to bridge protections one by one to find the course. first make sure all fluids are on level and coolers are clean. fanbelt tension and coolantthermostat can also be wrong.

Your 500kva generator doesn't work that means it doesn't generate electricity or fails to start?

If it is these two reasons, you can get help from he following articles:
https://www.dieselgeneratortech.com/generators/why-generator-wont-produce-electricity.html
https://www.dieselgeneratortech.com/diesel-generators/why-diesel-generator-fail-to-start.html
https://www.dieselgeneratortech.com/diesel-generators/diesel-generator-start-up-failure-causes.html