It seems I've accidentally turned on something so as I type the new typing appears but it gobbles up the text ahead of my cursor.

This means I can't insert any new text, and is very scary watching my text disappear!

It is probably a very basic command but I can't find it.

Your help will be appreciated.

You've probably toggles Word's overtype mode 'on'. The letters 'OVR' are probably no longer greyed-out on the status bar. Click that or press the 'Ins' key to toggle the overtype mode 'off'.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Oh, thank you so much!
I didn't know the word 'overtype' and all I could think of was 'delete'.
I'm back on track now - much appreciated.