BetterPHP

Well, then change your query to match your table
[syntax=sql]WHERE `username` = 'something' AND `password` = 'something'[/syntax]

they do match [syntax=php]$checklogin = mysql_query("SELECT * FROM users WHERE username = '".$username."' AND password = '".$password."'");[/syntax]

1 guy told me that i have to go through the check if the submit button is clicked in the form

Basic debugging. Start at the bottom and work your way to the top (looking for expected results). Along the way of echo'ing values and checking if values are set you will run across your error where the actual result is not what is expected. Once you get this debugging concept down, you will never have to post topics like this.

there is a problem i cannot find any errors -.-

If there are no errors then check on the condition statements you are using. Check that everything that you are checking with isset() is actually set. Make sure to check spelling and case.