My honda accord 91 wont start it only cranks. I have changed the spark plugs and it worked,the distributer and it worked for a week, i checked the main relay and it still dont work. What could it be?

Have you checked your fuel pressure at the fuel rail? Fuel pump or pressure regulator could be failing

How can you check that?

There should be a shrader valve on your fuel rail(looks like a tire valve stem). Attach a fuel pressure gauge there. If no valve you will most likely have to loosen the fuel line and have someone try (bump)to start it. Use caution if pump is good fuel will go (shoot) everywhere.