Site down - 404 error

My http://community.oxenhopeparishcouncil.gov.uk/ sub-domain site on this network is down (returns 404 error). Had been working fine for a couple of years! I've tried all the usual (disabling all plugins, deleting htaccess, re-setting permalinks etc.) but can't find the problem. Help!

The site is mapped to http://oxenhope.org.uk/ - the domain DNS includes the wildcard and the mapping has been working fine for years too. Nothing has been changed.

Support access has been enabled.

Ken