WIN NT 4 CRASH

one of my WIN NT 4 Servers, I installed WIN NT4 several time, it works properly one or two days, then after it crash or not booted .. i.e. after blue screen server restart again n again. then i re-install Win NT 4. but after one day or two it occure again. No errore massage displayed. may any one suggest me, why this problem occured? All hardware in my server is in working condition.