Have you applied the 4GB patch?
Also make sure your GPU drivers are up to date.
No i haven'tHave you contacted Dovetail support team?
Ok will try it thanksThere seems to be an issue with Train Sim with the latest Nvdia graphics drivers update release. Try doing a clean install of an older version of your graphics drivers, or a clean install of the latest drivers to make sure it isn't due to a corrupted driver install.
Ok thanksIf what magic said doesnt work contact - http://dovetailgames.kayako.com/