well easy way to fix that is reinstall winamp and your other players and that should overwrite nero again ... also I dont use nero six caused me problems but that is my own opinion ...if you dont wanna to do that
you could always go to my computer and then tools and folder options and then go to file types then find each file Example MP3 and just click change and pick what program you want to open it
third choice ...each mp3...cda ... audio disk you play when it starts up nero ...close it then go to that file ..right click and then properties and pick open with and choose what program you wnat to open with ...it will be the exe ..sometimes you have to go out to the folder ..example winamp folder ..then put check mark box in the always remember ....
but I would go first route it is easier and should reassociate all those settings for you .... if not do it the other ways
hope this helps ya