Sorry to hear you're having some issues. Unfortunately with technology, this happens from time-to-time. You can file a support ticket
here and we'll get you fixed up ASAP. All tickets are replied to within 12 business hours - though it never takes that long.
Alternatively, try using the VLC Player as Daugava suggested. You may also want to try downloading a fresh, clean, new copy of Quicktime Player (free) at
www.quicktime.com.