Have you used sulphite, and did not overdo it ???
Too much sulphite could inhibit yeast and then it will
take longer to start the fermentation.
Did you use sulphite ???
If you did the wine will be safe from spoiling for some
time so do not worry to much now.
Did you pitch the yeast or make a yeast starter.
Making a yeast starter helps starting a vigorous fermentation.
If you do not know how to do it read here:
http://wijnmaker.blogspot.com/2007/08/gist-starter-yeast-starter.html
If you make a yeast starter and it is fermenting vigorously add half the volume in must to it.
Wait till it ferments again and then add again half the volume in must
etc etc etc until the whole must is fermenting.
I presume acidity and SG are in the right range ???
Hope this helps a bit
Luc