What did Paul mean when he said the Gentiles had no hope and were without God?

Paul meant that while God was dealing with Israel on the Old Testament covenant basis, Gentiles were outside Israel's commonwealth and covenants of promise. They were without Christ, strangers to those promises, so they had no hope and were without God in the world.

Les explains that Paul is addressing Gentile believers' past position. At that time, Israel was still under God's promises in the Old Testament economy, and God was dealing with the Jew only. Gentiles were called uncircumcision by the circumcision in the flesh made by hands—often regarded as uncircumcised dogs. Paul carries it further: they were without Christ, aliens from the commonwealth of Israel, strangers from the covenants of promise, having no hope and without God in the world. Les notes that people get shaken by this and say God was not fair, but God is always fair, just, and righteous.

Ephesians 2:12

That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:

Why were the Gentiles without hope and without God in the world?

Gentiles were aliens from the commonwealth of Israel and strangers from the covenants of promise. God was dealing with covenant promises that belonged only to Israel, so Gentiles had no rights or access to them, leaving them without hope and without God in the world.