I bought a used Bosch Bulldog hammer drill on the internet some time ago and discovered it's not hammering. It will drill be almost no hammer action. Any suggestions?

There is an o-ring on the striker that will wear down over time, this needs to be changed, of worst case the striker has stuck in the hammer piston. Both these repairs should really be done by a service center as these hammer drills are complicated to repair if you are not familiar with them. Any Bosch service center will be able to help you. Just go to the Bosch website and find a center in your area.