[ubuntu-uk] Nautilus won't 'Display' after upgrade

[mac]

Just upgraded my desktop and laptop from Gutsy to Hardy.  Sadly, desktop 
upgrade left several things not working, so may need to do clean install 
:-(   Laptop upgrade went OK; but there's a problem with Nautilus that I 
can't find a fix for, despite lots of searching, and I'm pretty sure one 
of you guys will know the answer immediately.

It's simply that when I click on an executable in Nautilus, it asks, as 
always, whether I want to run it or display it.  But when I click 
'Display', nothing happens, as if Nautilus does not know which 
application to open it with.  I can still right-click and select 'open 
with text editor' and it displays in gedit OK, so not a big deal.  But 
irritating.

So I'd be grateful for advice about how to reset the default text editor 
for Nautilus.

TIA

Mac