Hello and welcome to justanswer.com my name is XXXXX XXXXX X'm here to help you with your TV problem.
Without the remote it is tricky where you could press the "menu" button and then unlock the TV.
However I do have a note scrawled in my workbook about something that you could try.
Press the Channel up button on the TV and at the same time press the Volume up.
If that doesn't work try the Channel up and Volume down.