A variety of connection problems can be resolved by the following steps:
- Close the MTG Arena client
- Open a Windows command prompt (cmd.exe) as an administrator
- Type ipconfig /flushdns and press enter
- Type ipconfig /registerdns and press enter
- Type ipconfig /release and press enter
- Type ipconfig /renew and press enter
- Type netsh winsock reset and press enter
- Restart your computer and launch the MTG Arena client