@sc version?
@sc bring it up in safe mode. If it sleeps, it's something in your boot options, if it doesn't then it takes a reg edit or a deep dive of your power settings to find.
@sc intel box?
@sc 2 things come to mind. Under power settings there is a 'media sharing' option that may be default to 'do not let idle'. Or its a setting under the intel device driver for your gpu.
@electricplatypus desktop