PHP Cuts out

I'm running a Windows XP Pro Server, with Apache 2, and PHP4.

My problem:
My PHP scripts, when given too much to do, sometimes cut out. Forums work great on my server, but when I do things that invole ( for example: opening more than 5 directorys with opendir ), it opens them and reads them to arrays, but then when I try to echo it in large scripts, it will not finish sending the data. Like, if I try to echo some links, it might show like this:

<a href="somelink">Sometext</a>
<a href="link2">seo

And cut out in the middle of nowhere. Its getting to be bad, it even does it on my phpinfo(); stuff ( http://66.75.198.235/php.php ). Sometimes it shows more, sometimes it shows less.

Any reasons why it would do this? It does it with more than just opendir, too.

Thanks.

Check the Apache error and access logs to see if there is any information as to what is happening.