After installing Sitelok I can’t login to the control panel

After installing Sitelok you should be able to go to http://www.yoursite.com/slpw and login with

username: admin
password: letmein

If after logging in you still see the login form (with no authentication failed message) then the most likely problem is that your hosting company has not enabled PHP sessions. Most do enable PHP sessions by default but there are one or two that don't. Check with the hosting company about this and let us know what they require.