Sharepoint hosted app in visual studio does not build

Hi,

I have a sharepoint hosted app with a workflow in visual studio 2013 prof., sometimes the when I build the app it shows only "Build Started ..." and nothing from on. I'm sure there is no build errors in the project. Even waiting 10-20 minutes does not show any progress. Cleaning the project doesn't work too.

How can I fix this issue ?

Thanks.