First, check to see if there is anything in the chamber.
Next, make sure you're using 7.62x39 in a 7.62x39 gun. Check the charging handle side for the caliber marking.
If those first two are Ok, then just put a round in the magazine, pull back the handle all the way, and release it, don't "ride the bolt" into battery. It won't hurt your gun to let it cycle as it would during firing anyway.