Could someone tell me how to watch AVI files? WMP won't play them :<

Do you have the latest version? =\ WMP should play them.

I don't think Windows Media Player stopped playing ALL .AVI files all of a sudden. You're probably just missing a codec for a certain file.
What does WMP tell you when you open a .AVI?

Anyway, you might just try VLC to play video files (or only that certain .AVI that won't work).

download the codec at www.divx.com for free, and next u will be able to see them.

Taxista, it could virtually be any codec, but it's probably going to be DivX though :)

It says "Error loading codec" :P

Search for codec packs on kazaa or something, if you find a file of around 3-4 MB, download and install it. These packs have almost all the codecs you'll come across.

Some have viruses packed with them, so scan them first.