Some GNU/Linux computers seem to have problems connecting to projectors. While my earlier ThinkPad R51 always obeyed Fn+F7 combination to turn on output to an external projector, recently acquired R52 did not.
After some research I found that XRandR has good support for output hotplugging. Although graphical tools are available to do this, I found the following commands useful.
% xrandr --auto % xrandr --output --auto
The first one usually works, and it has to be issued as the same user running X, and not root.
In rare cases when parts of the screen is cropped due to the projector having a smaller resolution, use the -s option to reset the resolution:
% xrandr -s 1024x768
Running xrandr without options would show what is going on with the screen modes.