Lets try a quick power cycle to see if that helps.
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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