she starts then she stops

I replaced my fuel pump and have been driving her for eight days no problems. I got ready to go to work and she would not start, so I automatically thought the pump was no good. The next day she cranked up, so I drove her for about thirty miles and came back home. Then I proceeded to go again and she did not crank. I was wondering if it was a bad fuel pump would it start and stop like that or could it be some other problem.