So, look up the page at my post and check that the pistons will extend and compress the pads. If so, and if you have a firm lever, I suspect that your pads have been contaminated. It's fairly common for someone to spill lube or brake fluid on parts and it only take a little bit to ruin a set of pads. Replace the pads and clean the rotor with alcohol and a clean rag. Also, if you pull the caliper and fully extend the pistons put a couple of drops of lube (Tri-flow, brake fluid, etc) at the base of each piston. You'll only need a 2-3 drops and you have to be careful to avoid spilling any on the brake pads. Sometimes pistons will bind up a bit and a little lube helps free them up.
Post an update once you've tried some more troubleshooting.
Mike