There are two things that you must check:
1.Ensure that the user account has the administrator privilege.
2.Disable the UAC (User Account Control) as it restricts the certain administrative function needed to run the web server.
To ensure that the user account has a administrator privilege, just run lusrmgr.msc from a Windows Start > Run menu to bring up your Local Users and Groups Windows. Now Double-click on the user account that appears under the Users, and verifies that it is the member of the Administrators.
To disable the UAC (as an administrator), from a Control Panel:
1.Simply type UAC in a search field in a upper right corner.
2.Click on the Change User Account Control settings in a search results.
3.Drag a slider down to the Never notify and click on OK.
Now open up a User Accounts window from a Control Panel. Click on a Turn User Account Control on or off option, and just un-check a checkbox.