Woops...I posted a whole different answer until I looked more closley at the sideways picture.
Looks like the roof above has a sidewall flashing issue. Your overhand would keep water from entering the top of the window. The water is probably coming in above this area.
Getting on the roof, if you are comfortable with that...is the next step. Then get us some more pictures.
Or call a roofer. The house may also have damage in the wall, get a professional to take a peak.
Can you see anything in the attic?
Let's figure it out.