1995 Honda Civic Dx, 1.5 L engine. Cranks, but won't turn over. I have heard the main relays on these cars go out often. No check engine light on. I have checked the fuel pump and do have fuel pressure. I have replaced the rotor and the spark plugs, and no luck. Any other suggestions?

If the CEL comes on and goes off normally, focus on the distributor. Usually, this means replacing the ICM and coil:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-4.html#post265896

Well if you are getting spark to the spark plugs then most likely it is sensors or e.c.u sensor ! I would start with the sensors or small stuff because that is most likely your problem.

Where and what is the icu sensor for a 1995 Honda civic

There is no "ICU Sensor."