1.First create modeline with your resolution
cvt 1680 1050
This will create modeline for resolution of 1600×900 which will look something like this:
1680x1050 59.95 Hz (CVT 1.76MA) hsync: 65.29 kHz; pclk: 146.25 MHz
Modeline "1680x1050_60.00" 146.25 1680 1784 1960 2240 1050 1053 1059 1089 -hsync +vsync
2. To add this resolution to monitor settings, type the following command:
xrandr --newmode "1680x1050_60.00" 146.25 1680 1784 1960 2240 1050 1053 1059 1089 -hsync +vsync
3. Next show your monitors list and find name of your monitor (VGA-1)
xrandr --listmonitors
3. And next write this command:
xrandr --addmode VGA-1 "1680x1050_60.00"
4. In Linux Mint, xorg.conf is not present by default and has to be created. This can be created only when x server is not working ie. in console mode otherwise system will give error. Type these highlighted commands one by one in console mode:
Alt+Ctrl+F1 (switch to console mode)
sudo service lightdm stop (For Mint 12 Lisa users)
or
sudo service mdm stop (For Mint 13 Maya users)
sudo X -configure (generates new xorg.conf file)
5. To switch back to graphical mode, type:
sudo start lightdm (Mint 12 Lisa users)
sudo service mdm start (Mint 13 Maya users)
If above commands fail to bring back graphical mode, just restart your computer.