A reliable player with built-in codecs get VLC if only as a backup player:
http://www.videolan.org/vlc/ (choose nearest mirror site)
Sounds like you may need xtra
CODECs; a list of locations to get them here (choose one or the other): 1.
Free-Codecs.com, 2.
Nimo’s codec pack, 3.
CoDecs & codec identifiers, 4.
K-Litecode Codec Pack