Difficulty downloading el Capitan

I installed a new hard drive on my MacBook Pro, reinstalled from Time Machine, and am trying to download el Capitan (I have Yosemite currently) from the App Store. When I click on "download", it will not connect and that little round swirly thingy just keeps twirling. If I go to "purchased" in the App Store, it shows it as downloaded but is grayed out so I can't choose it. Any ideas?