Dell XPS 9550 shut down suddenly

My service tag is expired cause i bought my laptop two years ago, It shuts down suddenly when i reach to my log in screen or use a little time. I have to plug in to turn it on and i also change my battery cause i think my battery is the reason. However, it happens again. What is my issue? 

Especially, it doesn't happen when i use for a long time, it only happens when i reach to log in screen or use a little time