physoc on "Site not displaying (Error 500) after ftp sync"

Hello all,

Since ftp syncing my site with my local site, my website has not displayed, with Chrome displaying:

'The website encountered an error while retrieving http://www.physoc.org.uk/. It may be down for maintenance or configured incorrectly.
Error code: 500'

I know its still there since if I write in the direct url of an image I can find it (here
for example). I cannot access wordpress admin panel either.

Please could you offer suggestions as what the problem could be.

Many thanks,

Tom