What operating system are you using? What are your firewall settings? Are you running other applications that use port 8080?
When you say "some times web pages are not opening", do you mean that at time you can access the web pages and at other time you cannot? If that is the case, did you restart the app server? In other words: you bring up app server, access web pages just fine, bring down app server, bring up app server at some later time and then pages no longer accessible. Or is it all during one run of the app server? In other words: you bring up app server, then your can access pages, and then after a while you can no longer access the pages?
What is the output on the console when you cannot access the web pages?