I'm sorry to hear that you're having this issue.
If the monitor worked previously and this was a result of the upgrade, it may be possible that the driver for the onboard graphics card doesn't have an update that supports 1680x1050. You might check with your motherboard manufacturer to see if there is an update to that specific component on the motherboard.
I checked our site, and up to Vista is supported for our drivers.
I can check tomorrow to see if there is a different driver that might work.
I am using monitor Samsung Syncmaster 2253BW with VIA Chrome9 HC IGP, On Board Graphic Card to the Biostar P4M900-M7 motherboard. I recently upgrade my OS from vista to windows 7, and suddenly my monitor/ LCD display can not get the proper/ previous resolution 1680x1050. Can u help me rectify this problem thanks