Can't get full resolution on external display

Can't get full resolution on external display

I have read lots of reports of this issue but haven't found a solution
yet. I have a Sony Vaio notebook running Ubuntu 12.04 LTS in 64-bits. It
has an Intel I5 processor and Intel graphics controller.
It is connected to a Samsung 23" LCD display through an IOGear KVM and the
laptop also uses a Sony docking station. Connecting the display directly
to the display does not change the behaviour.
Two other computers, one a second Sony laptop using a docking station, the
other a Lenovo desktop, both running variants of Windows, are also
connected to the display via the same KVM. With both I have full
resolution.
As I indicated, I have read lots of reports on this issue, have tried the
various suggested solutions, but still have 1024x763 resolution where I
should have 1920x1080.
I should also point out that I have done a full update on the OS.