You have an easement by necessity since you don't have any other reasonable access to your property without the road.  Your neighbor cannot prevent ingress and egress (entry and exit) to your property and that is why you have an easement by necessity.  You can sue your neighbor for declaratory relief to establish your easement by necessity.If you were not in the process of selling the property and were going to continue as owner and the neighbor continued blocking the property with the locked gate, then an injunction would be an option to consider to prevent the neighbor from blocking access to the property.  An injunction would be an option because land is unique and an injunction would avoid multiplicity of lawsuits due to the neighbor repeatedly blocking the property.  The court would then balance the competing interests and the benefit and burden; the benefit to the neighbor if the road is blocked versus the burden to you if the road is blocked to determine whether or not an injunction is granted.