If it still doesn't work try re-install the client.
If still not work, make sure your firewall system are off and enable the setting to allow it to run MU.
1) Uninstall Mu from your hard drive
2) Download the Lite Package : https://rapidshare.com/#!download|72p8|3802269285|InfinityMU.Setup.2012.LITE.exe|203439|0|0
3) Re-Install the game and follow procedures
4) Make sure that Main.exe is added as an exception from firewall setting or if your lazy turn of firewall directly when playing mu
5) Make sure your system unit is compatible to play Mu
You should create your thread more detailed, is there a message or error that appear?
Send us a screenshot or a video, we need more infos to help you with your
problem, we can't read thoughts.