If the transformer is turned off and has never been turned on then there is no chance that it will be able to electrocute you. If the transformer is undergoing high tension then there is a big possibility that it will hold a lot of electricity available. Even a small amount of charge that is left in the transformer will be enough to electrocute you.
The strength of the electrocution will highly depend on the amount of energy that is still available in the transformer. Remember that a transformer that has been turned off is not a guarantee that it will not provide a shock to someone who touches it.