To make drag&drop folder visible within AmiBroker: Tools>Preferences>AFL and at the bottom check "Show hidden folders". Then it is visible in "Charts" sidebar.
@hangye
I think your old layout is gone once AmiBroker is closed since auto-save is checked by default.
But next time:
Save your chart(s) as a local or global layout and give it a name (or save it as default).
Uncheck Auto-save Layouts in Tools>Preferences>Miscellaneous.
Et voila once you accidentally close a chart or a pane just double click your created layout again and it will be restored. Just create a test layout.
If you make changes to your layout that you wanna keep in the future then you have to right-click your layout and click "Save" every time since auto-save is deactivated.
If you check auto-save layouts in tools-preferences then all layouts are auto-saved before/during shutdown of AmiBroker or during switching to different layouts. So if you don't want auto-save being active then un-check it in Tools>Preferences>Miscellaneous.