Smart object are Image file types. Image file types should open in the application associated with the image's file type. Most image file types are support by Photoshop and associated with Photoshop and will open in Photoshop. However, all Image file types are not supported by Photoshop. Raw Smart objects should open in Adobe Camera Raw. Vector Smart Objects should open in Adobe Illustrator if Illustrator is installed on your machine. If you can not open any Smart object. Check your user's temp disk space see If Photoshop has created the Temp Smart Object work file. If it has make sure that image file type is associated with a default application installed on your system.