Hi, and thanks for choosing JA!
Unfortunately, Games Fever has not revealed the rules for this question, so no one knows the accurate answer, or even how to compute it. We can assume that yoyo's are allowed to be formed using boggle style rules, or even "tetris piece" shaped combinations. In that case, there are well over 100 yoyo's.
You may be interested to read the following page:
(if you can't get that to work, you can try: http://18.104.22.168/search?q=cache:994GRn_jSm8J:gamesfevertv.blogspot.com/2007_04_01_archive.html+http://gamesfevertv.blogspot.com/2007_04_01_archive.html&hl=en&ct=clnk&cd=1&gl=us)
There is no conclusive answer to this question, and until someone calls into the game show with the right answer we won't know. Even once they call in, it may be impossible to determine the rule system that was used.
I hope this helps. And I hope you are the person to call in with the correct guess!