I'm using Ubuntu Linux (Lynx) and till today Google Chrome was running perfectly well. But today I got an update, by the Ubuntu Update Manager, and I had trouble with videos. Most of them say "missing plugin" and others can be seen, but with no audio. I'm new in Chrome and I don't know what to do in order to get Chrome 5.0.375.55 beta working as good as before. Any idea?

What kind of videos? Flash or embedded?
Check about:plugins for the appropriate plugin to see if it's installed.
If it's embedded..I've always had trouble with Totem (not even just as a browser plugin). I uninstalled Totem and just installed VLC, I think it's working now but I don't really remember.
If it's flash you'll probably just have to reinstall flash..