I've seen a lot of people are having this issue right now and my friend just downloaded the game last night and is also having trouble however...
I was just talking my friend through this a minute ago. I told him to uninstall it then go find Microsoft .Net Framework 4 even if you already have it go redownload it and it should also give you a new file called Microsoft .Net Framework 4 extended. He did this and it started working finally. I hope this helps some people. In beta they were good about letting us know that we needed this. I don't know why it's not a link with the download as it is. Good luck.