The end of life of php4 is the end of this year. Your web host will be forced to upgrade of get left behind.
They might already have php5 available, either through your control panel or through a statement in a .htaccess file. Check with them if and how you can switch to php5, or what their plan is to upgrade (this is not an "if" they are upgrading, but a "when" they are upgrading issue.)
If you are learning PHP, developing PHP code, or debugging PHP code, do yourself a favor and check your web server log for errors and/or turn on full PHP error reporting in php.ini or in a .htaccess file to get PHP to help you.