What was found
AFTER TAKEOFF UNABLE TO PRESSURIZE AIRCRAFT. CABIN WAS CLIMBING AT 2000 FPM EVEN WITH 3 PACKS TURNED. ALL DOOR WARNING LIGHTS ON F/E PANEL AND CARGO DOOR LIGHTS ON PILOTS MCP WERE OUT. INSPECTION OF THE MAIN DECK REVEALED LOUD NOISE COMING FROM BULK CARGO DOOR AREA. A/C WAS DEPRESSURIZED IAW WITH FHB AND LANDED AT NEAREST AIRPORT. ON WALK AROUND, FOUND BULK CARGO DOOR OPEN. CLOSED DOOR AND PRESSURE CHECKED GOOD IAW MM 52-63-01 601 AND 21-31-00. OPENED A DMI FOR THE BULK CARGO DOOR WARNING LIGHT INOP.