Minimal Download Strategy in SharePoint 2013 ( _layouts/15/start.aspx issue)

_layouts/15/start.aspx is part of the Minimal Download Strategy in SharePoint 2013 which helps in improving the performance of page rendering. If you are having issues with it you can deactivate this feature at the site level using the below step.

Site Settings >>  Site Actions >>   Manage Site Features >>  Deactivate Minimal Download Strategy Feature.