The access check variable that is shown in the URL indicates that access was denied when you attempted to visit the index page. If you were entering the username incorrectly then the page should just refresh without anything in the URL. This tells me that you are failing the Administrator rule that is applied to the index page. The only thing this rule does is check the password you entered versus the password in the globals file. If you are failing this rule it indicates that the password you are entering is not correct.
As a quick test of the password go into the login page and go to line 50, add in two new lines and put this code in those two lines:
The value of the entered password is: <?php echo isset($_SESSION["AdminLogin"])?$_SESSION["AdminLogin"]: ""?><br/>
The value of the global password is: <?php echo $WAGLOBAL_Admin_Password ?>
After putting this in place and saving the page test it out. When you attempt to login and are taken back to this page it should list the password you entered and the value from the globals file for you to compare against.
This should get you going on the rite track, keep in mind that whatever your password is in the globals file will be listed here on your admin login page so this should only be done as a test, you should not leave this in place on a live site.