Logging on

My son just got his Inspiron laptop for his birthday. Because he’s only 10, I used my email to set up his computer. Last night he was able to logon with his password and had no problems. Tonight, after the computer turns on, the username and password boxes never appear. If I click or press any key, the computer goes to a black screen and after 45 seconds will come back to the initial screen. We cannot log on. How do I resolve this?