I agree with Hosfac about trying a different browser. I had numerous problems when I used IE. I started using Google Chrome, which has been wonderful. The only times I have issues is when the actual website is having problems.
Another thing to try, is make sure you are logged into the game launcher. Start the game up. Once you are on the main page click on the menu (3dots) and open the downloads dashboard. It may minimize your game so the game launcher can open. From there it will show your purchase history and what you have downloaded and installed and what needs to be. It can take a bit of time that way, my download dashboard "freezes" on occasion but it always catches up and is fine. If you do try it that way, I strongly suggest that you click on no more than 3 items at a time.
When I use the download dashboard, I open the launcher and then use a shortcut to start the game, that way I know the launcher is still open and will make the downloading much smoother.
Here is a link to the topic on how to start your game not using the launcher, in case you need that. Good luck!