Changed my LG L70 (MS323) runtime from Dalvik to ART and my phone's not working properly. Help?
ART is experimental at this stage, unless you're on android L (Lollipop) I wouldn't recommend using it.

If you are stuck in ART you can get back to Dalvik by following this thread: http://forum.xda-developers.com/showthread.php?t=2707841

Your device should boot then.