arduino uno r3
On pin 3.3V there is no any voltage, it is because board is defective something has to be done ?
With uno I work first day, usually I work with STM32F, I am able to mesure voltages in range of single microvolts. From your answer I assuming 3.3V should be when I connect uno to PC using USB.
without any work on board
Sounds like the 3.3v reg is dead. Either replace it, or accept that you have no 3.3v (this may also kill external power, because I think the 3.3v output of the reg is used as a reference voltage for the opamp that controls the input power switching - they divide the external voltage by 2 and compare to 3.3v to decide if the external power is ok)
I make a mistake, instead connecting 3.3V to Aref i connected it to pin beside it which is ground so good news - 3.3V is not dies when is shorted.