n5110 keyboard problem

i have a dell inspiron n5110. it is about 16 months old... but few days back its keyboard started acting weirdly. g key does not work when i want it to. but sometimes it is pressed automatically, and also the combination of left shift and t button doest not work at all(right shift and t works fine and t button works fine alone but does not work with the combination of left shift....and also left shift works alright with all other keys).. sometimes it starts to work for sometime and then it goes down and g button is pressed automatically. i ve reseated it and also changed the keyboard(i m out of warranty which is local by the way) but new keyboard only worked for an hour or so then it also started to behave in the same  manner as the old one... i m now out of warranty and also there is no dell centre in my area. plz help me and tell me wat to do... external keyboard is working fine and also the onscreen keyboard is working fine.. there has been no spillage or anything on the laptop..