|Is it a CRT or LCD monitor?|
If it is a CRT then it is a well known symptom known as "pincushion effect", for which there is unlikely to be any adjustment externally. It can only be repaired by an expert and there are dangers inside that remain after the monitor has been unplugged for several hours. Repairs (if anyone is prepared to take it on) would cost more than the monitor is worth. Prove whether it is the monitor or not by trying your monitor on a friends machine or trying theirs on yours. If it is a CRT I would be very surprised it is anything else than the monitor itself at fault.
SEE FOLLOWING POST - SEEMS THERE ARE LIKELY TO BE EXTERNAL MONITOR CONTROLS AFTER ALL (IF IT IS CRT).
If it is an LCD it is a whole different ball game, which is why I am asking.
Ms Hulot's boat