警告:mysqli_query()希望参数1是mysqli布尔值

After submitting something through my form I get the welcome part and then the mysql connection error because mysql is off, it goes away when I turn it on and then the boolean error. "Warning: mysqli_query() expects parameter 1 to be mysqli, boolean given in C:\xampp\htdocs\welcome.php on line 25"After submitting something through my form I ge