Check to ensure that no part of the mesh is intersecting the figure when everything is at the zero pose.

Ensure that you are not using double sided mesh or have polygons facing the figures skin. eg, turned back hems.

The simulation calculation should start within about two minutes and complete in under ten generally. If it does not start within that time then waiting longer, hoping and praying will just be wasted time. Best to cancel out and find out what is wrong.