Some users have reported an issue in which QuickTime content, including many MP3s, will not play in Safari 5.0.1. Users experiencing this issue often report receiving a QuickTime playback box with a question mark inside, which indicates playback failure.
In some cases, this issue is caused by problematic plug-ins. Quit Safari, then navigate to /Library/Internet Plug-Ins (the Library folder at the root level of your hard drive) and remove any recently added third-party plug-ins.
You may also want to try temporarily removing the following plug-ins:
- QuickTime plugin.plugin
- Quicktime plugin.webplugin
- VLC Plugin.plugin
After removing these items, restart Safari and check for proper operation. You can then add plug-ins back one by one to identify the culprit.
Reinstall latest version of Flash. In some cases, this issue can be resolved by reinstalling the latest version of Adobe Flash.