ON THE PREVIOUS FLT, THE PLT MADE TWO UNSUCCESSFUL IFR APPROACHES BEFORE LANDING ON THE THIRD ATTEMPT. THE PAX- CONFIGURED ACFT WAS LOADED WITH CARGO. THE PLT FILED AN IFR FLIGHT PLAN AND DEPARTED THE ARPT. RADIO CONTACT WAS ESTABLISHED WITH ATC AND THE PLT REQUESTED ACTIVATION OF HIS IFR FLIGHT PLAN. ATC COULD NOT IDENTIFY THE ACFT DUE TO NONRECEIPT OF THE TRANSPONDER. THE PLT WAS ASKED TO RESET THE CODE. THAT WAS THE LAST CONTACT WITH THE ACFT. IT WAS FOUND TWO DAYS LATER ABOUT ONE AND ONE HALF MILES FROM THE ARPT IN A HEAVILY WOODED AREA. UNRESTRAINED CARGO WAS FOUND THROUGHOUT THE FUSELAGE. THE PLT HAD BEEN ASKED TO MAINTAIN VFR UNTIL RADAR CONTACT WAS ESTABLISHED. RADAR CONTACT WAS NOT ESTABLISHED. THE WT & BAL COULD NOT BE DETERMINED DUE TO MOVEMENT OF CARGO. RECOVERED CARGO INDICATED AN OVER GW CONDITION. THE TIME OF THE CARGO MOVEMENT IN THE ACFT WAS NOT DETERMINED BUT BELIEVED TO BE POSTCRASH.