Out-of-date drivers and operating systems can cause a variety of issues, and are one of the first things to check when a game is having problems.
Troubleshooting steps for performance-related problems.
There's a problem with the connection to the Blizzard servers.
Troubleshooting for installation-related problems on Mac.
What to do if you have trouble with the captcha
Information on Unable to Locate Component error.
Troubleshooting problems with the Battle.net friends list
How to solve this problem on an incomplete Battle.net account
Troubleshooting steps for when a game installation or update is stuck on "Initializing"