I've got 27 10k potenciometers + 3x faders which are 20k. Now, just for the test, I've connected GND and +5V wires from each of them into Nano and one pot into first analogue pin. Now, the issue is that analogRead doesn't return 0-1023, rather, it gives me around 70 to 980 mostly. I even tried to connect the pots into another USB port (only GND and +5) and the results are the same. Any suggestions?
Measure the voltage at the pot wiper with a multimeter. If you don't get the full range from 0 to +5 then the problem is the pot.
I tried to disconnect the three faders (20k) and now I can get full 1023 but not 0, it gives me around 30.
Are you sure that one end of each pot is connected to Arduino Ground?