open your dashboard. inside, on the left, there is a small button. push it. now try opening your trunk. your trunk should open now. this button is used for when you valet the car. the idea is, you push the button, then lock your glovebox only giving the valet the plastic remote, but not the metal key. since he cant open the dashboard, he cant disable the trunk lock button, therefore cant open the trunk either.
my guess is you hit that button by accident.
hope this helps.