|1440 X 900 is a "widescreen" format (ie a widescreen resolution).|
The resolutions that are available are determined by the graphics adapter inside the PC (it's not determined by the monitor).
So it's probably the graphics adapter that does not support any widescreen resolutions, or at least not the one that you want. The only cure in that case is to install a new graphics adapter, often referred to as a "graphics card" or "video card".
Using a different monitor won't make any difference to the resolutions that are currently available from the existing graphics adapter.