Power Supply or Hard Drive

Hello, all
I have the following scenario: Computer with power supply 250W was broken and we got the same one. When, I am going to turn on the computer the procesor fan tries to run but finally doesn’t. I started to check all the connections and I found out that wehen I unplug the power from the HD and turn back on the computer. The computer turns on fine. So, why when I plug the HD power the computer does not turn on?

Thank for u cooperation