If you are sure you are not getting power to the board when you check the mains voltage then replace the mains input socket. It is possible this is making a bad connection. Swapping random things doesn't work, you need to be methodical and test from the mains input to the the output of the power supply at each stage.
Test the input to the power supply and if there is no mains AC there then work backwards,
To be honest, if you can't do basic voltage diagnosis then find someone who can and ask them to do it, it will save you a lot of time