The most common cause of this problem if you have a Power Macintosh is that you've accidentally turned off the extension "QuickTime Power Plug" in the Extensions Manager control panel. If you do this, QuickTime will have trouble playing music. It's easy to fix; open the Extensions Manager control panel and make sure that anything to do with "QuickTime" is turned on.

A second thing to try is assigning more memory to Holiday Lights, especially if you've added your own bulbs or music. Click on the "See Also" topic at the bottom of this page for instructions explaining how to do this.

If this doesn't help, something on your computer is probably incompatible with QuickTime Musical Instruments, which is an Apple Computer-supplied system extension that Holiday Lights uses to play background music on your computer.

If you're using RAM Doubler, this is the likely problem; RAM Doubler is not compatible with QuickTime Musical Instruments. The only solution in this case is to switch to normal Virtual Memory instead of RAM Doubler.

Also make sure that you have the latest version (4.0.3) of QuickTime. You can check this by opening your System Folder, then opening the Extensions folder, clicking once on the "QuickTime" icon, and choosing "Get Info" from the File menu.

If you have an earlier version of QuickTime than 4.0.3, you can get the latest version free of charge from Apple Computer at www.apple.com/quicktime.

If you have the latest version of QuickTime, try turning off other system extensions to see if the problem is caused by one of them. Choose Extensions Manager from the Control Panels item of the Apple menu, then change the current "Set" to be the "All" set for your System version (for example, "Mac OS 9.0 All" or "System 7.5.5 All").

If it works after restarting, it means the problem is caused by a misbehaving extension or control panel; turn them on one at a time in Extensions Manager until it stops working to see which one causes the problem, then let us know. We might be able to contact the author and provide technical information to them to correct the problem.

If it still doesn't work with only the basic extensions turned on, try turning off the music in Holiday Lights entirely to see if that helps:

As soon as you open Holiday Lights, hold down the SHIFT key for a few seconds. This will prevent Holiday Lights from playing any music or showing any bulbs. You can then choose "Music Box" from the Settings menu to turn on the music to see if it causes the problem, or choose "Bulb Factory" to show the bulbs to see if this is the trouble.

 
See also:
Holiday Lights is running low on memory. How do I fix this?