Sounds like kitty has laryngitis.
Laryngitis is an inflammation of the mucous membranes of the voice box. Signs of laryngitis include hoarseness and complete loss of voice.
The most common causes are excessive meowing and a chronic cough.
Other causes include tonsillitis, throat infections, bronchitis, pneumonia, inhalant allergies and (rarely) tumors in the throat.
Laryngitis that doesn't have a serious underlying cause almost always clears up on its own within a few days, but some cats need an antibiotic to get over it. If this has been going on for more than three or four days, it would be a good idea to call your vet for advice.