That sounds like a significant signal issue. A DVR won't boot without an adequate signal. Commands entered with your remote require communication with a Cox server and a response back. A weak signal will delay the response time and can also cause channels to be unavailable.
Schedule a tech visit to check your signal strength. If your cable comes in from a pole, be sure to ask for a tech with a long ladder when scheduling the appointment. Request the tech check your signal strength at the tap. Your issue could be caused by a weak main line signal that woud require it to be escalated to line technicians for repairs. Cox won't schedule that escalation unless the on-site tech reports a signal issue at the tap. If your issue is caused by a weak signal or a problem with any other Cox equipment, you won't be charged for tech visits.