Check, if your website is in UTF-8.
Just copy following code to the <header> tag of your documment:
<meta http-equiv='Content-Type' content='text/html; charset=utf-8'>
Or you can use just shorter version according to HTML5. Compatibility is fine:
<meta charset='utf-8'>
See difference between this two metatags: <meta charset="utf-8"> vs <meta http-equiv="Content-Type">
Or you can use header. This code place into your PHP code. The best position is at the start of the document.
header('Content-Type: text/html; charset=utf-8');
Or check if your file is in UTF-8. This you can do with your code editor. I use PSPad and i recommend it to try.