cs6 - Different colors and shadows when opening an image in photoshop and after saving the picture

I am working on Photoshop CS6 and i face the following problem.

When I open a jpg file on Photoshop CS6, the image appears to be much more dark than the original jpg.

If I start editing the picture in order to be brighter and then I try to save to a new jpg, then the result I get is completely different again: The new picture is bleached...

I try to open it with a different Photoshop version (CS5) but the problem still remains.