Cannot change screen resolution

Reinstalled windows xp home sp3
AMD 7750+, 2Gb DDR2, Gigabyte Geforce 9400GT.
Stuck at 640x480... I get the option to go to 1024x768, but it flickers then gives me 640x480. Monitor is AOC LM726.
Drivers are up to date. nVidia is latest 190. anything else?

Video card dying?

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Hope not, coz its a brand new card....

*** UPDATE *** Got it to change twice last night (after deleting and reinstalling drivers), but after playing a game it would switch back to 640x480 and stuck.

Just an idea :

Have you used the dxdiag command to check if any of the graphics files are corrupted . To do this click :

Start > Run > in the command box type "dxdiag"

Run all the tests and check that all Direct X files are functioning correctly