Swapped out light switch and now WIRES have no power?
I had an instance in my current home where the previous owner replaced a three way switch with a non-3-way dimmer and it acted like your situation.  The original switch would seem like it did not work, unless the dimmer was on, then it would switch the dimmer.

Take a look at the wires you have and also look at wiring diagrams for a three way light circuit and see if anything makes sense in that context.  For my situation, I had to remove three light switches downstairs where the bad dimmer was and figure out what every single wire did until I found the two travelers and hot that were meant for the original three way.

For now, also check your breakers.  It's possible that a certain on/off arrangement of your new switches is leading to a short that is tripping the breaker since it doesn't seem like you truly know what wire goes to what screw.