Resolution messed up after installing drivers

[Chooboo]

Hello guys.
Got a little problem here. After installing the latest drivers for my Acer Aspire 7551G(Ati Mobility Radeon HD 5470), my resolution gets wrong. Before installing the drivers, I always ran at 1600x900, but now the drivers can't let me run more than 1152x864.
Thanks for replies.

 

[rgd1101]

did you don't the driver from acer or amd website?

 

[Chooboo]

Now I got it from the Steam "Search for AMD driver update" option. I also had this issue a year ago, when I downloaded them from AMD website.