Missing pages

I have a website installed on BTConnect which I am still developing. It was working fine but now when I try selecting different pages from my menu it keeps telling the page can’t be found. If I republish the page it will come back again. The main page will come up fine and I can select any other page and it appears to work OK but if I then try to select another page ( even the page I am on it will tell me it can’t be found.
This is not a problem with my PC as it fails from a mobile as well. Any body else experienced this sort of thing. Is it my supplier, is it wordpress, is it a virus where do I start?