No backups?
You can generate your lists within the MameWAH menu interface by bringing up the options. By default you press P2 Start to bring up the options menu and there is a "Gamelist Options" item. You can use that to switch to other lists, generate lists and add/remove games from the lists.
You should generate the "All Games" list first, then and other lists you might have like "Favourites", "Classics", "Vertical", "Beat em up", "Shmups" etc
MameWAH has problems with generating lists from later versions of mame (is to do with the xml file format), although there is a version floating around where the issue has been fixed. Sorry for being vague, I can't remember all the details either, it has been a year or so since I redid my own Mamewah lists. If MameWAH won't generate lists for you, a 3rd party list generator like ROMlister can help.