startup problems

My Brother as a laptop windows 8 suddenly started getting a problem when he start the laptop and it in the logon screen before you get to the accounts or password screen, when he hits any key to get to the accounts screen the laptop goes into shutdown mode, any ideas?

It could shutdown because the battery level is low, or the harddrive has a physical error..

Was the laptop plugged in?

Try it again with laptop plugged in and all USB devices disconnected..