Please do the following steps and tell me results:
Make sure that WWW (word wide web ) Publishing Services Is started.
Control Panel ->Administrative Tools->Services->Scroll Down at the bottom list
*Open Administrative Tools->Internet Information Services Manager->(Server Name)->Web sites->Default Web Site->
Right Click Exchange->Select Browse.
Can you see OWA Page?
If not, What is the message?
look in Administrative Tools->Event Viewer->Application Log some warning/error about Exchange / WWW services.
Do you have other (s) web services in this server?