Resolution reset.

Hi, i'm having a problem. Few days ago i turned on my pc. Lauched DiRT 2. My game resolution was set to 800x720. All games was set on that resolution. My dekstop resolution was 1280x800. But when the other day i turned on my pc, my dekstop resolution was okey but when i launch any game, DiRT 2, Grid, Call Of Duty Modern Warfare 2, resolution was the same, but didn't stretch to the edges of my monitor (Laptop HP Compaq 6735b). Then i made a restore from point which was made after my last Windows Update (I'm using Windows 7 Ultimate). Then in games resolution was okey, 800x720 stretched to edges of my monitor. But everytime i turn off or restart pc My desktop resolution also changes to 800x640. Hot to fix this?

Thanks in advance.

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