directory dtructure for skecth

After installing (tried twice) IDE (version 1.5.8 windows) on Windows 8.1, when i start arduino, the response is

" Arduino non può avviarsi perchè non riesce a creare la cartella dove salvare gli sketch"

I searched similar problem in posted messages, but without results; may be it's a my error, sorry.

Thanks giorgeny

for those who do not speak Italian "Arduino can not boot because it can not create the folder to save the sketch"