rgPaiva:
Yes i connected a wire from A0 to GND directly too, and tried the ReadAnalogVoltage program, but it shows only 5v. And i havent tried the 54 digital pins , only the pwn outputs, but i think the problem is with the ATMega2560 ;/. And it doesn't have any shield on it, and i am using it on wood table.
What about the other analog pins? Did you try A1-A5?