blank page pops when i try to connect to database to create a simple login page using php and mysql using xampp

I have used the following code but when i click on the login button i'm redirected to a blank page.in this i have created a login pAGE that checks if the user is present in database.i have not given a sign up page instaed manually added values to the database.in sign-in.html i have given the form and in connectivity.php file i have given the code to check if user and password are present in database. as per code the output should have been "succesfully logged in" or "error could not login" but instead i get a blank page.how do i resolve this.please help!! the php file that connects to db