Hello everyone.
We’re currently looking into this, as we received several reports about it.
Meanwhile, please make sure you follow all the steps from this guide, as it is made specifically for this issue:
battle.net/support/article/18769
If the steps didn’t help, please let us know and post a DxDiag of your system:
battle.net/support/article/12988
You can post it in a paste page like http://pastebin.com and provide the resulting URL here.
How did I do? Let me know!