swapping the yoke wires is a way to do it if all else fails, but if you are not comfortable soldering and playing about inside a monitor (with the 25KV on the anode and all that) then it's not for you,
(you may be able to find a TV tech to do it, if any exist where you live.... round here they are all board swappers, when a lcd/plasma screen goes down, all they do is swap the boards/modules out with new ones, if it dosent fix the fault, they write it off, half of them dont know which end of a soldering iron to hold, the other half wouldent know what a soldering iron was if it was stuck up their arrr....

anyhoo, have you tried pressing CTRL ALT and an arrow key yet???
that works on all my machines, my 4 month old netbook with obviousely on board gfx, the 2 year old laptop, GF's 1 year old desktop and the mame computer which is about 4 years old,
mind, i only found out about it the other day, i way playing a game using the keyboard, ctrl and alt are fire, arrows direction, drove me mad when it seemed to randomly flip screen rotation, thought it was a bug in mame or something,
then i figured out it was the combo of those keys triggering it, very handy to know now,