you have to make sure two things are turned on:
- Global Illumination within render settings in Cinerender and you have difuse depth of 2 (if it's configured on 1 it won't cause any light reflection and if it's more than 2 it will incredibly increase render time)
- Check the material of the glass in the window (more specifically you have to check the transparency channel. color should be black not white and brightness should be 95 because if it's set to 100% you will lose the feeling of a glass and it will look like air)
hope that would help