Originally Posted by ellacharm3d
The Custom music channel has always been wonky and never work right.
Do these mp3s work outside of Sims? In VLC or WMP or iTunes, etc...?
When you placed them in the Custom Music folder, did you remove the pre-existing ones?
You place them in Custom Music folder in Documents or the Programs path?
The readme.txt (via the Start menu) has some notes on MP3s being in a specific format, otherwise they don't work.
You could also try if the MP3s work in a brand new "The Sims 3" user folders, by renaming the current one.
One last resort that I saw work, is that the user created a brand new Windows User Account - shows that something in the user folders were conflicting somehow.
Stereos are also buggy if on EA's default StoryProgression. You need a mod that periodically turns off stereos in Inactive Households - like Twallan's Overwatch or Awesomemod or any other little mods that does this specific task.
You just need to ensure whichever one you chose, do not clash with what mods you already have.
Also, have you ruled out hardware issues by updating audio drivers?