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 connection problems
What to do if you can't claim a beta key for a Blizzard game.
Troubleshooting steps for disconnections in StarCraft II
How to obtain error logs for Blizzard games
Troubleshooting steps for latency problems in StarCraft II
Information on what to do when a game update is stuck at 0 B/Ss
Information on moving Blizzard games to a different hard drive
Information about troubleshooting problems with the Blizzard Battle.net friends list
Follow these steps to troubleshoot problems with your low-speed or wireless internet connection.