Check for .htaccess file and other dot files. Rename them to htaccess.txt to temporarily solve it.
I can think is my old blog is stopping it from working as its linked to the same website. Is there anyway to fit this?
Check the .htaccess and whether you have changed the siteurl from www to non-ww version, for example.
If you have not disabled or blocked cookies required by the site, then the issue is with Apache. Ask 1and1 in that case.