Pages not fully loading

I am stumped and so is my hosting help desk (shared server) on this one. My site is on a php4 server, with database. Recently I have had pages not fully load, and it seems to be a symptom that is spreading to other pages in the site. I have considered the following causes and dismissed them: - .htaccess page - there is very little in it - php.ini file - is old and the problem is new - mail function causes delay which times out the php rendering ... still wondering about that one, but the help desk reports that it works quickly. I wonder because in some though not all the instances of the problem, the page renders to the line just before the mail() function - a recent change to the script caused the problem - no, because I have loaded older versions and they also have the problem, these pages were working for a few years, though I have updated regularly I am pretty sure this is a recent issue. - it is my computer or connection - no, the help desk and others have noticed the problem - it is the server - well the help desk don't think so. I notice the pages can: - partly load, often to the same point but sometimes to different points in the script - not load at all and be not found, - load but incorrectly with the php arguments missing (to explain: an enquiry page has a form that submits to the same page and it should come back and say thanks etc, but it comes back with the form but without some of the pre-set element like the product the form was enquiring on). - re-load correctly on refresh, or partly load more, then fully load. - problem occurs both with IE and Firefox. I have tried putting print ("test line x") throughout the script, which just showed me it was failing sometimes before the mail function, but not always, sometimes in the middle of a loop to create a select box it just stopped rendering. Has anyone had this strange and frustrating experience? john