There are many possible solutions for your problem, i'll write some of them below
1- You did not install ASP.net when you installed iis
2- Press start-> search for services and start asp.net
3- Server.cfg-> billing server should be smth like :
/
4- Your iis default website path is not configured correctly, it should be c->inetpup->wwwroot
5- There is no iis files in wwwroot
6- Maybe default website is stopped?
Try all the solutions above, if non of them worked, feel free to contact me at skype : aeron.53