Well there are 2 things that you have at your disposal depending on what you need to do.
1) If you can upgrade to Fedora 7, do that. Hardware issues are generally kernel related, and going 3 revs is definitely changing your kernel. Also, if its not the kernel, a new version of ALSA may help too.
2) Drop to single user and manually update your system. Mind you, FC4 is ancient, and no longer supported. I am not sure what a 'yum update' will do for you.
If you are being told that you need FC4 due to a class or something, update anyway or reinstall FC4 in a vm (like vmware of virtualbox) on your Windows or Mac based machine. Linux has been perfectly supported on vms for ages.