Great question — answering as the UphillTech team:
All the light switches should have power at all times on one screw. The other screw ahould have power when switched on. According to your description, they don't. That means whatever is feeding the light switches is not doing so. If you have receptacles which are also broken, keep following the chain toward source. You may be a broken GFCI or the GFCI itself may not be getting power. It may be a problem with the neutral. It is almost assuredly one single problem. Double failures are very unusual. If necessary, undo wire nuts and measure voltage on each wire.
Full answer by Harper - Reinstate Monica: https://diy.stackexchange.com/a/108998 (CC BY-SA 3.0).
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