I found a blizzard support article that basically said:
- Restart your router
- Restart your computer
- check for driver update
- check your internet connection
However, that article linked to these two much more technical versions of items 1 and 2:
Article ID: 31851
Blizzard Support - Power Cycling Your Network Devices.
Article ID: 82450
Blizzard Support - IP Release, Renew, and Flush DNS.