There may be some kind of setting you have to change to pass both sound and video through the HDMI. Do you have any other cables attached to the blu-ray drive like sound out cables that would interfere with sound going through the HDMI? Read the manual or post the model number. I assume you are not using a computer if you connected the blu-ray to the TV.
What MAKE/model is the TV?
What MAKE/model is the Blu-ray?
Modern TV's have lots of settings on their menu and I guess Blu-ray players are similar. Sometimes there is a preferred HDMI for specific devices.