Resolution at Boot Up Issue

Ok so in the last week, when i come to the Vista Ultimate login screen my screen resolution has been downgraded to something like 1280x1024 or 800x600 automatically, very arbitrarily. Sometimes it happens, sometimes it doesnt.

I have the latest drivers for my graphics card (XFX GTX 280 XXX) and my monitor is a 22" Samsung Syncmaster T220 which natively displays 1680x1050.

As i said, this has happened in the last week, so it could be a software change or something? No hardware changes have been made to my machine for at least 2 months.

Any suggestions would be great, thanks guys.

Maybe you should check that the GPU is correctly inserted and not is "shaking", and after that reinstall the drivers, as Outlander said

Ill try reinstalling the drivers, the card isnt shaking at all, and im using the official samsung monitor drivers.

Thanks.