Thanks Saab, I too came across that likely solution but that didn't work either. Late last night I bit the bullet and did an up to date back up of all the data and reformatted the disc. Clean install and the keyboard works!
The irritation is that as in all the cases of PC glitches if I knew I would have to do a reinstall then I would just get on with it but because most glitches can be fixed with a bit of perseverance, and this one seemed as if it should be quite simple, I instead wasted many hours before doing so!
Thanks for all the contributions, much appreciated.