I'd inspect the latch to see if it's sticking, and not fully disengaging. Barring that, if you don't hear the solenoid "pop" to open the trunk, it might be the solenoid itself that's not engaging properly. If it's a newer car (still under warranty) I'd just take it back to the dealer, that shouldn't be considered a wear item.
If it's not still under warranty, I'd see about having a handy friend pop the little cover of the trunk off, and seeing if there's anything stuck inside, or if the motor/solenoid for the trunk popper isn't getting power or is burnt out.