Novice requests help

I apologize for my lack of sophistication as this is new to me. I'm trying to convert .flv files to .avi files, using the SUPER freeware program. The conversion appears to have been successful, but I can't get Real Player or Windows Media Player to run them. I rec'd a suggestion that the problem may be tag files. I downloaded Mp3tag in an attempt to run these converted files through it, but I can't find a way to get my files entered into it for the program to run. Any help that you can offer will be greatly appreciated.

Mp3tag does not support .avi files.

I also don't think your issue has anything to do with tags.
Maybe you don't have the correct video codec installed.
You could install http://en.wikipedia.org/wiki/Ffdshow
or use a player that already contains many codecs like http://en.wikipedia.org/wiki/VLC_media_player