Still the lighting.....note the shadow 'cast' behind objects...such as the Start Menu....to the botton-right...ergo light source is to top-left....however your skin lighting contradicts that, being equally 'bright/hilighted' from both left AND right.
Remember...3D is an illusion, as is trompe loi .... your job is to fool a person's eye, not confuse it....

[Trompe Loi]