arduino giving garbage values for analog read from an externel power source

i made a project using an piezoelectric disk which generates alternating voltage of the scale of .1-.4 volts. arduino is giving nonstop values between to 1024 and then again to 0 repetitively. i even tried using an 10 k resistor but even that dosnt work i connected the two terminals of the piezoelectric disk one to ground and the other to analog pin A4 the ic is also having repetative problems.'till now 4 atmega 328 have had problems with the bootloader please tell the solutionn

arduino is giving nonstop values between to 1024

You have got problems.
Mine only go 0…1023.

Try putting the disc across a potentiometer, and see how that goes

i meant 0 to 1023 but it is supposed to give no voltage as the voltage given means stress is applied and no stress is applied on it the problem is that it works just fine for some time but then the problem starts

At what frequency is your signal varying? At what frequency are you measuring it?