A lot of times after server maintenance or if you are just having a hard time connecting to the game it's a good idea to power cycle the connection. This will clear out the DNS cache and allow the connection to build new connection information.
Here's how to power cycle:
1. Turn off all computers on the network
2. Unplug the power from the modem and the router (if applicable)
3. Wait about 1-2 minutes
4. Plug in the modem first and wait for it to completely boot up
5. If there was a router, plug the power back in and wait for it to completely boot up
6. Turn on the computers and try the game out
If that doesn't work try flushing the DNS: http://us.battle.net/support/en/article/ip-release-renew-and-flush-dns
Let me know what happens.
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