I have Snow Leopard installed on an old MacPro. I want to upgrade to Mavericks. When I go to AppStore-->Mavericks and click on the download button nothing happens. Do I need to install the intermediate releases (Lion and Mountain Lion - I think). If so, what is the process?
If the Mac Pro is old enough, then it cannot be upgraded beyond Lion. Check the listed requirements... My old Mac Pro 1,1 was in this category.
See the chart at the bottom, "latest supported OS" HERE
Just to check your doing everything right:
The download link should say Free and then Download once clicked on once, after that, press it again.
From there it should ask you for your Apple ID username and password.
Then it should start to download, as said above, Launchpad should have a progress bar on it's icon indicating something is downloading. Check the App Store for it too.
As stupid as this sounds, have you tried to restart your internet by unplugging its power for 10 seconds and reconnecting or even just checking your connection to see if anything is faulty?
It's a big update as shown above so unless you have enough bandwidth to download it your stuck.
Also another update for it came out Yesterday so it may be a good idea to try again.