Hi Amber,
It's not really normal, but it could have been a retro fit! We have old out side wiring for extra exterior lighting, for retro flood lights... and some of the built in homes lighting. The exterior wiring is run through conduit. That seals it from the weather.
If you hired licensed contractors to install your windows, there is no reason these days that they should have cut through electrical lines to, or in the home. Licensed contractors, normally take the time to look for these things.
Just my opinion, but I think that repairing the electrical issue, should be on their shoulders.
Maureen
![Cool 8-)](./images/smilies/icon_cool.gif)