Laptop Fn key not working after keyboard removal

I recently removed the keyboard from my laptop to clean it and now the Fn key doesn't work. Whenever I press the Fn key it acts as a mouse right-click. I don't think any other keys are working improperly. I reinstalled the OS as I planned to anyway and I still have the same problem. I have removed and reattached the keyboard many times but with the same results.

I know it might not have been a great idea to do this myself but I'm selling the laptop and I want it to look clean but I fear I may have permanently damaged it. Any and all help will be greatly appreciated.

My laptop is a:
Dell Inspiron 5100
Windows XP Professional