PS disk missing, can´t create any photos

Hi!

I´m trying to put another jpg image on top of another jpg image in Photoshop. I´ve always done that (whit these exact images also), and I have the jpg photos saved in my hard drive.

When I try to drag the second image on top of the other, Photoshop says "Dokumenttia ei voida sijoittaa, koska levyä ei ole" which means "Document can not be placed because there is no disk" in finnish.

Can someone please help me? 

I´m using Mac Book Pro.