ABS non function,brakes shuddering hammer noise, what's up?

My ABS non function has been lighting up on my computer screen, my steering column has been shakier when driving. The brakes have a shuddering hammer noise at times. Something is sticking down towards the rear of the underside, seems to have been dislodged (perhaps by a speed bump), any suggestions what I need to do?

Brendan Murphy
March 2010