It seems to have been a rainy or otherwise wet day there (judging from the moisture between the glasses), and that's not a good thing when trying to open a window with a wooden frame. It's probably the same thing I suffer, the window jammed now but as soon as the frame shrinks it will open all right. So, you'll want the frame to dry and...
Solution A: Wait for a hot and dry day and try again
Solution B: Take a hairdryer and proceed from there.
Hope this helps,
- R -