From my own experience this happens because of another windows service using the same port as the Qlikview Webserver service.
On our Server the Qlikview Webservice could not start because of the IIS admin service that was running at the same time, which also uses port 80.
By ending the IIS admin service(or other service using port 80) and restarting the Qlikview webserver service this problem was solved. If necessary, you could also probably change the Qlikview webserver port to something else such as port 8080 ,which could also solve your problem.
Hope this helps.