THE ENG LOST POWER SHORTLY AFTER THE PLT BEGAN A DSCNT. SUBSEQUENTLY, THE ACFT COLLIDED WITH TREES DURING AN EMERGENCY LANDING AT NIGHT. NO REASON WAS VERIFIED FOR THE LOSS OF POWER, THOUGH THE POSSIBILITY OF ICE IN THE FUEL SYSTEM WAS CONSIDERED. THE TEMP & DEW POINT WERE 8 DEG & ZERO DEG, RESPECTIVE, WHICH WAS NOT CONDUCIVE FOR CARB ICE. THE ACFT WAS FURTHER DAMAGED AFTER THE ACDNT, WHEN IT STARTED TO SWING WILDLY DURING A HELICOPTER SLING OPN & HAD TO BE RELEASED FROM ABOUT 300 FT AGL.