He believed that he had caused the deaths of the crew. When the plasma conduits overloaded during an ion storm, he left his post to protect his daughter, Liana, instead of trying to repair the injectors, reasoning at the time that his team might be able to handle the repairs but Liana certainly wouldn't survive the imminent crash. Every other member of the crew, including his wife Maya, were killed in the resulting crash.
He tried to repair his ship for many years without success. Finally, he created a holographic crew to ease his guilt and provide a family and companions for his daughter. When the Enterprise NX-01 crew discovered his ruse in 2151, he was persuaded to leave the planet with Liana. His ship was repaired and he and his daughter were able to take off and return to their homeworld. (ENT: "Oasis")