How to suppress page number?

You could use \pagenumbering{gobble} to switch off page numbering.

To switch it on afterwards, use \pagenumbering{arabic} for arabic numbers or alph, Alph, roman, or Roman for lowercase resp. uppercase alphabetic resp. Roman numbering.

I had the exact same problem. What worked for me was \thispagestyle{empty} after inputting the title page, not before.

Maybe try to enclose your title page (or the input file) into a \begin{titlepage} and \end{titlepage}; and put \pagenumbering{arabic} just before your main body starts.