When you change your screen resolution in Windows XP, the Display Properties window disappears. You are unable to make additional resolution changes.
This behavior can occur if the Display Properties window is near the bottom of the screen prior to decreasing your screen resolution.
To resolve this issue:
1. Press CTRL+ALT+DELETE.
2. Press the Log Off button on the Windows Security dialog. You may have to press it a second time.
3. Log on.
4. Start / Run / desk.cpl / OK.
5. Select the Settings tab.
6. Drag the slider to the desired screen resolution.