Hiya, Thanks for all your replies.
At the moment DH haven't replied to my support request, but things seem to be working again and according to the error logs have been for nearly 4 hours, but as it 4am here on New Years day, the site could have only been accessed by myself in the last hour, so no real guarantee that it's all fixed until later on today.
Do you know what else could cause this kind error?
Or is it too vague to pin point an exact cause? My error log is full of lines like this "Premature end of script headers: /dh/cgi-system/php.cgi" which is why I assumed it to be something wrong with the php.
I am the only person with access to the files and nothing had been changed, so I believe it was nothing I done wrong that caused this.
Thanks again, and Happy New Year!