Sounds like you have an intermittent connection problem. To start, if the motherboard does not exhibit the same behavior with the power and reset button attached as not attached, it probably is not the MB; it is probably the buttons. But, if it does the same thing when you isolate the MB from everything else (disconnect buttons and technically all other hardware except CPU and RAM just for thoroughness), it is probably the MB or the PS.
Test the resistance of your power button with a multimeter. It should normally be infinite (usually read as "1") ohms. Then, with the multtimeter, push the button, it should read near 0 ohms.
Test your reset button as well the same way, it should exhibit the same behavior.
Also check to make sure the back plane of you MB is not shorting the power pins by reading the resistance across the pins, it should read something other than near 0 ohms; not sure what though could be high, could be low. Put a small smount of pressure on the board with your fingures at that location, and test resistance at the same to see if it changes, it should not.
Problem with your question is the power button and rest button typically (not always) do the same thing and usually can be swapped with each other. So if you swapped them, and it still came on right away, then either both buttons are bad or it is something other than the buttons, like a short on the back plane; but then it should have started and /or turned off with the buttons disconnected as well..
Could be you connectors themselves are bad also if the screwdriver works but the buttons do not and they test properly with a multimeter. You could do the same test to the buttons with them connected to the MB out of the computer and test the resistance of the buttons on the MB itself, it should do the same things as above. Infinite resistance usually, 0 when button pressed.