It soundsa like the mechanism that alows you to open and clase the window has broken .theres a metal strip which runs around the inside of your sash window this holds all the bolts and opening arm . Sometimes the opening arm breaks away from the metal strip causing the window to jamb.If this is the case when you eventualy get the window opened you wont get it closing properly .
If the window has dropped and is jamming, adjust the hinges ,alan screw on the side and bottom of the hinges the bottom alan screw makes the window go up and down the side screw makes the window go left and right.
alex falkirk, September 2008
