Below you can find typical weatherproofing problems with windows and how to correct them:

1. There is moisture on the inner surface of the glass: the apartment ventilation is insufficient and the space is over-sealed (like a bottle). This means that replacement air cannot get in and extact ventilation doesn't work. Remove a few cm of seal from the top of the inner frame and the lower outer frame.
2. There is moisture between inner and middle frames: the seal leaks, it hasn't been installed at all or the window glass is no longer weatherproof. This can be caused by old glazing sealant or the window glass' becoming loose. To correct this problem you need to re-seal the glass with e.g. silicone. 
3. The outer glass is moist or frozen: the outer frame is over-sealed. Remove some seal by experimenting first with 3 cm strips from top and bottom so that the air can circulate and the moisture is removed. Too big gap will cause the inner glass to freeze so you will find out by experimenting.