CTRL S

This isn't CAD related but I'm stuck.
I have Office Pro Keyboard and at some unknown time the CTRL S decided not to function in any application.
I can't even insert a CTRL S into a shortcut area within programs.
All other CTRL fucntions work okay.

I have changed keyboards to no avail.

Word 2007 and other applications still show CTRL S as Save.

I've Googled till the cows come home, but can't find anything quite like my experience.

Any ideas gratefully appreciated.
Well so long as it doesn't require reinstalling Windows!
Win7 Pro, 32 bit.

regards
Richard