I presume that the first thing you did was to make sure that you were in Shaded With Textures display mode with X-Ray mode turned off. Right?

Next I would ask, what happens when you first start the program and start a new model? Is the display still limited to wireframe or is it normal?

Beyond that, especially if you're running Windows Vista, you could be experiencing problems resulting from inadequate OpenGL support. See this thread:
http://groups.google.com/group/sketchupissues/browse_thread/thread/1616fdc5a0e93fe9#

-Gully