If you say you have pulled out the dead roots,I think there would have been tubers attached to them,so you will probably have to start again with new ones..You could always scratch around gently,to see if you can find any..but maybe you would be seeing new growth now,if that were the case..

Yes, as bloomer says.....seems like they may have rotted.Although, mine, in pots outside are only just starting to shoot.