DRG ARRIVAL, THE PLT WAS CLRD FOR A VOR RWY 35 APCH. ALSO, HE WAS ADVISED THAT THERE WERE PROBLEMS WITH THE RWY LIGHTS &THAT OTHER PLTS HAD MADE MISSED APCHS THAT EVENING DUE TO DIM ARPT LIGHTING. HE WAS THEN CLRD TO UNICOM FREQ & TOLD TO CANCEL HIS IFR CLNC AFTER HE HAD LANDED. HOWEVER, BEFORE LANDING, THE ACFT CRASHED ON LVL TERRAIN APRX 1/2 MI NORTHWEST OF THE ARPT WHILE IN A LEFT DESCENDING TURN. AN EXAM OF THE ACFT & ENG REVEALED NO PREIMPACT PART MALFUNCTION/FAILURE. RADAR DATA INDICATED THE ACFT HAD BEGUN A 360 DEGREE TURN AT ABOUT THE TIME IT CROSSED OVER THE THRESHOLD OF RWY 35. SUBSEQUENTLY, IT CRASHED WHILE TURNING THRU A HEADING OF ABOUT 240 DEG. APRX 9 MI SSE AT THE DULLES IAP, THE WX WAS IN PART: 1700' SCATTERED, 2200' BROKEN, VIS 3 MI WITH FOG. WITNESS STATEMENTS & A WX STUDY INDICATED THERE WERE AREAS OF FOG AROUND THE ARPT WITH THE VIS AS LOW AS 1/2 MI. THE REIL LIGHTS & THE PLT CONTROLLED LIGHTING SYSTEM HAD BEEN INOP SINCE 5/15/86, BUT NO NOTAM HAD BEEN ISSUED. THEREFORE, THE RWY LIGHTS (MIRL SYS) HAD BEEN PRESET ON MEDIUM INTENSITY.