Aspect ratio problems....

My wife has a notebook with a Benq monitor attached. Uses single display with monitor as primary screen. Aspect ratio is fine on the notebook, but when she tries to change the ratio for the monitor, nothing happens. It used to until this morning. The drivers are up-to-date. She reinstalled the Intel graphic accelerator driver, so this is not the problem.
Can't find a way to change the aspect monitor for the monitor screen. She has tried display in control panel and also in intel graphics itself. Nothing changes and all stays stretched out over the screen.
Any clues gratefully received.