On June 19, 1998, at 1908 central daylight time, a Cessna 310N, N5030Q, received substantial damage when landing on runway 36 (5,000' x 75' dry/asphalt), near Janesville, Wisconsin, with the nose landing gear not extended. The pilot said that the airplane had just been painted and the nose landing gear door was not properly attached after painting. On retraction of the nose landing gear the nosewheel became trapped by the door and could not be extended again. The pilot reported no injuries. The 14 CFR Part 91 flight was operating in visual meteorological conditions. No flight plan was on file. The flight departed Watertown, Wisconsin, at 1810. Examination of the airplane after the accident revealed that the linkage for the right nose landing gear door was not secured. When the landing gear was retracted on the previous departure, the nose landing gear became trapped and inoperable. Repeated attempts to extend the nose landing gear were unsuccessful and the airplane landed with the nose landing gear not extended. The accident flight was the first flight after the airplane had been painted. The nose landing gear doors were disengaged during that maintenance.