Crack the bleed screw and press the brake pedal. See if you're squirting fluid. If you are, you know your master cylinder and lines are good. If your pistons aren't moving, perhaps when you pushed them back into the caliper they are now seized or cocked sideways in there. If you have a high enough pressure air compressor, you can remove the bleeder screw and blow air in there to hopefully push the pistons out. Put a piece of wood or something else in the caliper to catch the pistons so you don't shoot them all the way out of the caliper.
If you aren't getting fluid out of the caliper, you could have some crud or something else blocking the lines from pushing fluid back up. Keep moving up the lines to check if you are getting any fluid pressure when hitting the brake pedal. You may just need a brake fluid flush.