i suddenly cant play avi files no more on my wmp???

i got xp and it used to work until a few days ago...

when i try to open any avi file at all it says : cant open file,filetype unsupported

it does the same at other players....

i already reinstalled wmp and reinstalled codecs... but that doesnt seem to work

how can i change this so it will work again???

do i have to reinstall xp again ????