Screen at not the right resolution in Linux Mint

Hi everyone,

I have two monitors both at the resolution of 1680x1050 and they work fine in windows 7. however, whenever I boot into Linux Mint one screen has the correct resolution and the other is at a default resolution of 1152x864. When I go on to 'display' in system settings the correct monitor which is a dell has been recognised but the other one which is a ViewSonic monitor is labelled as unknown.

I have updated my drivers on my GT 640 nVidia card and that has not solved anything. The monitor is running off a VGA cable and is VGA-0 when I type 'xrandr' in the terminal. 

I would be really grateful if someone could possibly help me and if you could give me any suggestions what to do.

Unfortunately I don't have a HDMI cable/adapter to see if the resolution changes. 

I do believe that the fault is due to the monitor not being known but I'm not sure how to change that.

Thank you for your time. 

BTW I am new to Linux and have been very happy with everything else other than this problem.

Well, you could find out if its a cable problem by switching cables from that Dell monitor. From what i heard, Linux has some issues with multimonitor setups, might be worth checking dedicated Linux forums. Guys over there always tried to help me.