left front, drivers side rear brakes locked. Changed calipers now no brakes.

Sir / Ma'am. Caliper replacement would require a brake fluid bleeding procedure, some calipers can be installed backwards, resulting in a bleeder screw being located on the bottom, rather than the top, of the caliper,, making bleeding the brakes impossible, as air rises to the top. Please, for your safety, and the safety of others, consult a professional.