I'm having some problems with analog input. I'm using an Arduino Mega2560 and I had working a temperature controller with an LM35 sensor. The analog input A0 was working properly, but now without nothing connected to the arduino board, I have 4.6V in A0, and the temperature controller is reading this value instead the value offered by the sensor.
Any idea?, I used a 19V power source for the board and peltier module. The A1 pin has 3.6V and the others seems to be ok you can mesure 0.xV.