Looking through the user guide and there is no reference to screen size, other than when playing games.
http://www.sonyericsson.com/cws/download/1/249/972/1216894082/S500i__UG_R3a_AE.pdf
Try resetting the phone (but keep the data and files)
From standby select > Menu > Settings > General Tab > Master Reset > Reset Settings (do not select Reset All or your content will all be deleted), then wiat for propmt and press Continue. You can also remove and reseat the battery afterwards as well.
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