If you want to register the game on Impulse, you will have to download and install the impulse client.
After that, you can go to the My Games tab and enter your key (you should have recieved a unique software key when you bought the game).
After Elemental is added to your games list, you can install it by choosing install from the list.
What OS are you running?
I've seen this issue with Windows XP when the "Windows Firewall\Internet Connection Sharing (ICS)" Service is disabled. Many people disable the sevice instead of just disabling the Windows Firewall. Disabling the service will have the same effect as disabling the Windows Firewall, but it will also cause some programs to fail their install. If that service is disabled, try to enable the service, then install the game. If it installs correctly you can disable the service after the game is ready to play.