I was just going over the history of comments here. I see some of you are in a tough spot. My suggestion, bring a lawsuit in common pleas court - or whatever the entrance level court is in your area. Usually it is for claims under $10,000 or so. You do not need an attorney - you are better off without one. The judge hears the claim, and most of them will go out of their way for a non lawyer type.
The fee is usually nominal - $25 or so - and if you win, you get it back. If nothing else it will get the attention of your neighbor, and possibly of their window manufacturer who may respond on their behalf. See if you can figure out which windows company we are talking about. If you are in the typical development, it will be the same one that made your windows. Include them on the complaint. Most places will let you do service by mail - a big savings as well.
That is what I did for our homes.
We WON! Well - not really. They settled for a smaller amount. So . . . claim the max you can.
Let us all know how that works out. Thanks.