If you're refering to music then get a backup player: QCD: http://www.quinnware.com/

If you're refering to video then get a backup player: VLC: http://www.videolan.org/vlc/ (choose nearest mirror site)

Both these programs use in-built codecs & play amost all.

For video it might also be worth getting GSpot: http://www.headbands.com/gspot/ which will tell you which codec you need.