98 Maxima engin change problems

I changed the engine in this car and it runs fine when you can get it started but that is the problem on start up it will turn over but the starter will kickback and all power is lost for a split second and then go again and repeat this sometimes it will finaly start and sometimes it wont I have put a new starter on and replaced all the crank and cam sensors and it has made no change in anything the engine is the same as what I took out I even put a new computer in this thing I dont know what else to do to this thing any info would be a big help thanks