maybe your missing the brake lines? do you get any sorta pressure at all? Did you happen to check for leaks when bleeding the system? When replacing one caliper you only need to bleed that one caliper. You don't have to bleed all 4 in order. Make sure your bleeding in the correct order. If you have ALOT of air in the lines for whatever reason its going to take awhile to bleed the system completely. Have someone help you and start with a big bottle of brake fluid.