ADC is not working properly

I'm currently working on an Arduino Uno. Recently, I noticed that the analog pins of my Arduino board can't read values more than 910. Whereas the range for Arduino Uno is 0-1023.
I realized the problem by taking values from a variable resistor.
What might be the causes and what steps should be taken?
Now that my Arduino has become faulty which I suppose, should I do all the projects taking range 0-910?

Measure the voltage on the high end of the resistor. My guess is that you're only putting 910/1023 of 5V = about 4.5V.

No, I am sure its a problem with my board because I have tested the resistor. Moreover, if I change the board without altering the external circuit then it works as expected!

I didn't say it wasn't a problem with the board- it may be a problem with that board's 5V only being 4.5V (assuming the resistor gets its high end voltage from the board, you didn't say.)

What does it mean that you "tested the resistor"?

What does the ADC read when you connect an input only to the 5V pin?

Irrespective of the actual supply voltage, it should read 1023.

(deleted)

ShetLand:
I didn't say it wasn't a problem with the board- it may be a problem with that board's 5V only being 4.5V (assuming the resistor gets its high end voltage from the board, you didn't say.)

If board supply is 4.5volt, and you put 4.5volt on the analogue pin, you still get 1023.
Leo..

Wawa:
If board supply is 4.5volt, and you put 4.5volt on the analogue pin, you still get 1023.
Leo..

AWOL already pointed that out

AWOL:
Irrespective of the actual supply voltage, it should read 1023.

I have found out that my Arduino board can supply at best 4.49 volts instead of 5volts. maybe that's why ADC doesn't display more than 915 volts.
Thanks to all. So should I conclude that there is a problem with the voltage regulator of my Arduino board?
if yes then how can I fix this?

If the potentiometer was connected between the Arduino 5V pin and ground, you wouldn't have a problem
getting to 1023.

How are you powering the Arduino board?

Are you powering other devices from the Arduino 5V pin?

No I am not powering any other devices.

Abid_Shahriyar:
I have found out that my Arduino board can supply at best 4.49 volts instead of 5volts. maybe that's why ADC doesn't display more than 915 volts.
Thanks to all. So should I conclude that there is a problem with the voltage regulator of my Arduino board?
if yes then how can I fix this?

The reference voltage for the ADC is Vcc, so if you connect the ADC pin to Vcc you should get a 1023 reading regardless of whether Vcc is 3V, 4.1V, 4.49V or even 5.2V. Did you try this already?
(yes, I'm the third to point that out).