Have you tried 're-training' the switches?
If the window moves at all they can start to lose their stored positions for 'top' and 'bottom'.
If this is the case then take the window to the bottom extremity, keep the DOWN button pressed for 5 seconds to re-train the computer. Put the window up and keep the UP button pressed for 5 seconds.
The next time you try it the computer should remember the top and bottom positions.
If the switch(es) don't work at all, could be a fuse?
Mark Hankins, August 2008