please I need help changing resolution

Im running XP and I had my PC hooked up too my samsung lcd TV but now I have put it back on a 4:3 monitor in my kids room the resolution wont change from 768 I keep moving the slider along and apply the new settings but it wont change can anyone help me?

thank you in advance for any help

On the Display Properties screen, make sure you have the right display selected on the display drop-down-box.