missing "=" after &dvdid
comment out the header and just print out your link to make sure your variables have values

I commented out the header in this page, but I am still able to add products to the cart, but when I also comment out the header in the shop page, then its not doing anything

my mistake

on on your shoping page view the source of your buttons and confirm that they have values by each param

echo "<a href='AddToCart.php?DVDID={$DVDID}&name={$name}' class='customButton'>";

should translate to something like this

<a href='AddToCart.php?DVDID=1234&name=dvdname' class='customButton'>dvdname</a>

if you're seeing this

<a href='AddToCart.php?DVDID=&name=' class='customButton'></a>

than the problem is on your button generation not passing the params

yh, but I am passing the parameters right, unless I am not passing it correctly?