THE ACFT COLLIDED WITH HILLY TERRAIN APRX 6 MILES EAST OF THE ARPT DURING THE SECOND ATTEMPTED ILS RWY 10 APCH. THE PLT STATED THAT COMMUNICATION AND NAVIGATION PROBLEMS WERE EXPERIENCED DURING THE FLT. HE ALSO STATED HE CHANGED FUEL TANKS EVERY 1/2 HR DURING THE FLT. A MISSED APCH WAS PERFORMED DURING THE FIRST ILS ATTEMPT BECAUSE THE PLT COULD NOT 'POSITIVELY' IDENTIFY THE RWY THRESHOLD. ON THE 2ND APCH, AFTER OUTER MARKER PASSAGE, THE PLT NOTICED HE WAS BELOW GLIDESLOPE AND NECESSARY ADJUSTMENTS WERE MADE. HE CONTINUED TO STATE THAT AFTER TIME PASSAGE HE NOTICED FULL DOWN GLIDESLOPE DEFLECTION AND MIDDLE MARKER PASSAGE HAD NOT OCCURRED. SHORTLY THEREAFTER, THE ACFT IMPACTED TERRAIN. THE INSTRUMENT PANEL AND RADIO PACK WERE REMOVED FROM THE ACFT BEFORE INVESTIGATORS ARRIVED. THE RT FUEL TANK WAS FOUND EMPTY AND THE LT WAS NEARLY FULL. NO MECHANICAL FAILURE/MALFUNCTION WAS FOUND. RECORDS INDICATE LAST TRANS CHECK WAS 5/9/77, LAST STATIC SYSTEM/ALTIMETER CHECK WAS 5/12/77. LAST VOR TEST COULD NOT BE DETERMINED.