What web browser are you using? Gmail supports Firefox, IE, Safari
etc. Find a full list at
http://mail.google.com/support/bin/answer.py?answer=6557&topic=1523 I
also have trouble with the music on e-cards, but since I find that
music annoying it doesn't worry me. I think Yahoo! Mail has that
problem too. Overall I don't have any serious trouble using Gmail with
Mozilla firefox so if you are not using it I suggest you give it a go.
Also try clearing your browsers cache.