What's the problem? And what's success - lots of profit or lots of attendance and happy parents/teachers? Is it lack of support from teachers/parents? Or that you desperately need funds? If your funds aren't too bad then I would concentrate on providing a really fun and good quality, value for money fair to try and get parents and children back on side. By that I mean make sure that the prizes are good, and that the odds of winning on tombolas are fair (but obviously not so great prizes and odds that you don't make a loss!)
Success for profits - Find a parent who is able to get matched funding from their employer for charitable work. Lots of big companies do this. If that parent can be involved in the raffle, or a big money earner like the bottle tombola (by involved in, I mean a 30 min volunteering slot) then it can double your profits for that stall/activity.
People generally like the old favourites - bottle tombola, children's tombola, lucky dip, Santa's grotto, cakes and tea/coffee (mulled wine if your school would allow it) and lots of good, well thought out games for the children.
Other ideas:
Used teddy tombola (get a pop up tent and kids get to go in a pick a teddy)
Human fruit machine
Biscuit decorating/Craft table
Second hand book stall
Secret room (where children choose and wrap presents for their parents)
Have a grand finale? Have the school choir sing some carols?
Lots/All of these depend on the generosity of parents in terms of donations and time in volunteering to help run stalls though.
I think its tough for lots of people at the moment and sometimes I think its good to show that the PTA are trying their best not to just 'fleece' parents but looking to fund raise outside the parent population. So you could see if local businesses could sponsor a stall for a donation. Or widen the invitation to the Fair to the local community. Or offer something that doesn't cost anything to parents, like having a free storytelling room of Christmassy stories?
Good Luck!!!