Dell Inspiron 7537 Keyboard Mapping

Hi

My Inspiron 7537 has been working fine since bought from new in September 2014. However, last night the keyboard mapping appears to have become corrupt:

"e" maps to "PAGE UP";

"c" maps to wireless control/airline mode;

"7" maps to "9".

These are the only that are incorrect that I've noticed so far... the rest work as expected. An external USB keyboard is working as expected.

There have been no spillages or accidents over the keyboard.

Any suggestions?!?

Cheers