External monitor not detecting correctly, Resolution issues

Hey, Im using a Samsung Syncmaster 2033 LCD external monitor with my 15" mid 2012 Mac book pro via thunderbolt x VGA cable. Normally it detects the monitor and scales it to the right resolution which is 1600 x 900. But these days it just shows up only as "VGA display", and the resolution is all wrong. The closest option i get to choose from is 1600 x 1200.

I have tried clicking on "Detect Display". But it doesn't help. Whenever i have had this issue in the past, i would just restart the computer, and it seemed to have worked. But not anymore.

PLs help.