Did you get a confirmation email that the room is guaranteed to your credit card on file? If so, call up the Marriott Platinum line and bring this issue up with them. As long as you didn't cancel it, they should pay you compensation (probably $200 for Autograph Collection) and relocate you to another hotel.
Either contract Marriott via the Contact Us link on their website or call them up and let them know about this. The room should have been guaranteed to your credit card. The reservation should still be on file but if you have an email confirming it you can give them that as proof. Let them know the hotel cancelled because of the MLB All Star game during that period.