Quicktime player can't open much of anything of use...

Not sure if this is an OS issue or something else, but since I upgraded to Mavericks I can't tons of files anymore, MOV, AVI, WMV's...nothing will play on my system, i've even tried downloading perian, flip an dither utilities. I'm not having any problems with display or sound.... I can play DVD's no problem.

No matter what i do with digital files (AVI, WMV, even MOV!) things aren't working.... i get errors "not a valid file". I've even tried VLC and VLC2 (hence Perian). I can play the same files on my Windows machines .... any ideas? Hoping it is something stupid.

Much appreciated

Have a look at this. https://itunes.apple.com/us/app/free-mp4-converter/id693443591?mt=12
or try this http://support.apple.com/kb/ht3678