“The Thirteenth Floor” examines this enticing and ominous possibility. On the thirteenth floor of a corporate tower, visionaries Douglas Hall (Craig Bierko) and Hannon Fuller (Armin Mueller-Stahl) have taken virtual reality technology to its apex by creating a living, breathing simulation of 1937 Los Angeles on a computer chip. When a confused Hall awakens to discover a bloody shirt in his house and Fuller murdered, Hall becomes the prime suspect. Did he do it? Why can’t he remember? Is there some connection to the virtual world?