Theme Corrupted or Lost – Please Help!!

Hi,

I was trying to edit my ‘style sheet’ when everything froze up. I had to close the screen and re-open, when I tried to return to ‘Appearance’ / ‘Editor’, I get the message ‘The requested theme does not exist’.

Somehow it has been removed – along with the structure of my site.

Is there a way to re-install this one part without having to start again?

Your help is much appreciated.