THE LAST COMM WITH THE FLT WAS WHEN THE PLT CONTACTED ELKO RADIO AND REQUESTED THE SALT LAKE CITY WX. HE REPORTED THAT HE WAS AT 11500 FT AND VFR ON TOP. THE SPECIALIST ON DUTY WAS UNABLE TO PROVIDE THE WX INFO DUE TO A COMPUTER SYS OUTAGE BUT RECOMMENDED THAT THE PLT CTC CEDAR CITY FLT WATCH FOR WX INFO. NO REC OF ANY FURTHER CONTACTS BY THE PLT COULD BE FOUND. APPROX 1 HR LATER, A WITNESS RPTD SEEING ACFT LIGHTS AT A LOW ALTITUDE HEADING IN A SOUTHERLY DIRECTION, NEAR THE CRASH SITE. THE WITNESS STATED THAT THE WX AT THE TIME WAS SNOW AND ICY CONDITIONS AND THE STATE HWY PATROL CONFIRMED THAT BLIZZARD CONDITIONS EXISTED IN THE AREA. EXAM OF THE WRECKAGE REVEALED THAT THE ACFT DESCENDED INTO THE DESERT IN A SLIGHT NOSE DOWN, STEEP RIGHT WING DOWN ATTITUDE ON A TRACK OF 170 DEGREES. NO EVIDENCE OF MECH FAILURE/MALF OF THE ACFT OR ITS ENG WAS FOUND. THE PLT HAD A PRIOR HISTORY OF HYPOXIC PROBLEMS. THE ALT AT WHICH HE LAST REPORTED WAS IN THE AVERAGE SUB-HYPOXIC RANGE.