rear disc brake piston won't budge  

I was replacing the brake pads on my 1994 Honda Civic. It has 4 wheel disc brakes. The front end went fine. When I tried to change the rear brake pads I couldn't get the piston to budge at all. I don't have a special brake piston tool so I use a C-clamp. My first C-clamp bent so I got a different, larger one. I cranked so hard on this one I broke the clamp in half!! Still, the piston wouldn't budge at all. If I get a special piston tool will that work or is there something wrong with the piston? Do I need to replace the rear pistons (since this is the same on both sides)? Do I have to first disconnect the ABS and emergency brake before I can push in the piston? I put the rear brakes back together after some cleaning but I am going to need to replce the pads. I really don't want to have to pay $50 to a garage to do something I can do myself. Any help would be greatly appreciated. Thanks!! You can e-mail me directly at mike1969@windstream.net