Yesterday (and today) it simply wouldn't complete bootup. It's OK in safe mode - including safe mode with networking. We've gone back to the previous restore point - and run the startup repair procedure - and run the check of C Drive - and run a memory check - all to no effect. Our C Drive used to have only Windows on it - but with Win7 it also has a few programs on it - they don't always allow a choice to install elsewhere (very unfriendly).
Currently we're running an Avast check (in safe mode) but really don't know where to go after that. We're getting closer to having to bite the bullet and do a full reinstall - but that takes some time to reinstall and reconfigure everything so we'e reluctant to do that. Thus any suggestions gratefully received.