Alternatively my computer gets hang at begin

hi dear,
my computer works fine but sometimes,alternatively my computer gets hang at the beginning when showing intel then i have to press restart button to continue,then it works fine.when i open my computer,it works fine but then next time when i open it,it gets hang at the very beginning when showing intel at the left top of desktop.this thing happens alternatively.
please tell me the best step by step solution to correct this problem,that will be urs most kindness.thanx