You're not giving us much to go on.
So you've definitely got more than 750 music files?
How are you adding them to the playlist? (there's plenty of different methods)
What file format are these songs? eg. all mp3, a mix of mp3, flac, wma, ogg, etc?
Is support for all those file types installed?
What version of Winamp?
Winamp Pro/Full, or Lite?
Have you installed any extra 3rd-party Winamp plugins, and if so, which ones?