Does anyone know what would cause my text to display oddly?

Sometimes on a page some words are not words. Other times the entire page is affected. They are boxes with numbers and letters in them. A square a little bigger than a capital letter with four numbers and/or letters. Two on top of each other. Firefox has the numbers and letters while ie and Chrome just have the boxes. Is it possibly a setting somewhere is not correct? It happens in emails as well. Any ideas? It's starting to drive me crazy.