Toshiba equium m70-339 -

Question

I have an 18 month old Toshiba laptop, no warranty and the "s" key has stopped responding. I changed the keyboard and the problem is still there. Everything else seems to be fine. I've updated the bios and that didn't change anything. Do you have any ideas about what I should try next? Its been suggested that I change the motherboard - if I do this is the problem likely to recur - this seems to be an issue with Toshiba laptops. Someone else suggested it may be the ribbon that the laptop attaches to as with a bit of jigging about the "s" did put in a brief appearance.

Thank you for your time

Paula