Harddisk problem. I know nothing of computers but when i boot up the computer it is telling me

Question

I know nothing of computers but when i boot up the computer it is telling me that the 3rd master harddisk or harddrive can't remember which is status bad backup and replace or press f1 to continue. when i press f1 it just boots up normally and no messages appear telling me that anything is wrong. it is also a intermittent problem as sometimes the computer boots itself up no problem.