First, try resetting the sound & video (if you haven't already done this), i.e. go into the menu, select "Reset" and press the right arrow key.
If you haven't already looked at the troubleshooting steps in your manual, this is worth a check as it lists a range of possible reasons and things to try if the sound or picture stops working. The troubleshooting section is on page 80 and the manual can be downloaded here.
As you can get into the menus, this means that its lamp (the bulb which projects the picture) is still good.