did you put the code in the right file to read the instructions for the browsers to show the favicon?
IE takes 3-7 days to show the favicon.
firefox can take 3 hour to 3 days.
as the favicon is the same named file no matter what image is used, and the browser has already looked and put the default one up, they do not check everytime you load a site page to see if it changed, as they are all called favicon, and it is not stored in the cache, you can not clear it to force it to show.