How to install mysqli (Fatal error: Class 'mysqli' not found) NO mysqli section in phpinfo()

Question

I am making a website on my local Windows computer that uses php and mysql. I get the error:

Fatal error: Class 'mysqli' not found in [site-url]\includes\db_connect.php on line 4

Line 4 is:

$mysqli = new mysqli(HOST, USER, PASSWORD, DATABASE);

I have read many other questions, all of which say to install mysqli or edit the php.ini file. I am running this on php 5.5, and the php website says that mysqli is installed by default on php 5.3 or later. My php.ini file includes:

[ExtensionList]
extension=php_mysql.dll
extension=php_mysqli.dll

I'm not sure what I am doing wrong. My phpinfo() has no section for mysqli. The only time the word "mysqli" ever even comes up is in the "credits for php" section.

I would appreciate any help. Mysqli should be installed but it looks like it may not be. How can I install it on php?

EDIT: Just to reiterate, there is NO MYSQLI SECTION in my phpinfo() page. Other questions (such as the one of which this was marked a duplicate) have a mysqli section in their phpinfo().