System turns off suddenly after turning on for few seconds to 5 minutes

Today after turning on my hp elite desk pc, I was transferring movies from my phone to pen drive using pc directly and suddenly the system turned off. Then when I tried to turn on, at first it didn't turn on,after a few seconds when pressed the power it turned on but again after some time it turned off. It is continuously repeating. Sometimes it turns off aftermore than 5 minutes, but sometimes it turn off after a few seconds