Photoshop Elements 7 Serial Number Invalid

I have an old copy of Photoshop Elements 7 I am attempting to download onto my Surface Pro, however my disc drive is not working and I downloaded elements off of the adobe website. It installs perfectly but when I go to enter my serial number, there is a red x next to the serial number and the prompt claims that my serial number is not valid. Why is this occurring? My Photoshop Elements disc and serial number came with an old Wacom Bamboo tablet if that makes a difference.