it's a corproate PC on a domain.
previously had windows 7 pro, upgrading (in-line) to Windows 10 Pro previously.
working fine with no issues until now.
all the settings (either set by group policy) or manually configured appear to be indentical to all the other PCs (which have had the same upgrade process and are the same make/model).
clearly there is something on this system that is stopping windows update and microsoft store from connecting, but what that is appears to be a mystery. everything else on the PC is working correctly.