I have two ceiling mounted lights just above the hallway upstairs. The lights are controlled by three light switches, one at the bottom of the stairs, one at the top of the stairs, and one at the other end of the hallway. Recently the one switch at the top of the stairs stopped working, yet the other two switches continued to work with no problems. I replaced the one defective switch and the lights worked fine for a few days regardless of which switch you use. Then, suddenly, the switch that I replaced stopped working again, but this time the other two switches also stopped working. Now all three switches will not work. What did I do wrong?