PHP = Blank pages

I have some PHP pages on my site which I paid someone to create.
They usually work, yet sometimes they result in blank pages. Is this due to an error in the script, or due to high site traffic slowing the server? Or to something else?

Without an error message it is hard to say, unless you show the code.

If you do “View Source” in your browser when you get a blank page, does anything appear at all?