no command dead robot

has your phone been installing random apps? if so press the off button and the lower volume button at the same time until it turns off. If it says no command you could try pressing the off button and lower volume together. If this does not work it is better to take it back to the place you got the phone from and explain what happened then he/she would possably be able to fix it. If not you will have to get a new phone.

hope this is useful.