PowerPoint 2000 and Windows Media files

Ever since I’ve inserted new .wmv files in my powerpoint presentations. powerpoint has been screwed up. Either the videos show up as red x’s and/or the command buttons don’t work and I need to use the menu command also the slide will not advance without forcing it out of presentation mode. This is occurring on more than one file and more than one machine. There are no viruses and we are running Windows 2000. Thanks.