Any major differences between this shop and the other one that publishes fine?

I think a restart computer is a first point of call

Lots of windows updates recently and i have had a few issues since.

If all else fails try opening a new WINDOWS user account and publish from that, this trick cures lots of issues for me, if it works make sure you close old user account after transferring everything.

Then if Viv's suggestions don't work give that pc a swift kick in the electrodes.
But I'm still wondering if you can publish the other shop without the same problem.

I had exactly the same problem only yesterday. There was no activity at all just the blank box and no error messages. It turned out I had the server settings pointing to the wrong directory on the server, it was staring me in the face but I did not see it for hours. Also it would be worth checking the URL address in the 'Your Shop' settings cos I had that wrong as well .

These things are so easy to get wrong and sometimes difficult to trace but good luck.

Phil