Hey guys,
I had this exact same problem, it went from not showing some of my games, to not showing ANY of them. Searching this board I found the solution, however, my computers crashed since then and I can't remember what I did. But I do know this. It has something to do with a DAT file or something of the like which is compiled to tell MameWah what the games are, or something. I think like commandline Mame does this on its own, but GUI Mame32 does not. And some games work in Mame32 that don't work in commandline Mame.
So basically, there was a file that is with commandline Mame, or something that will extract information into a file you name and you need to move this file to the mame32 directory and use it and path the readout to the name of the file you need. And I know all this sounds good but theres really no answer here. I'm just hoping to bump this tread and find someone who knows what im talking about, otherwise, ill search the forum and see if I can find it and upate this post.