Last night at about 11pm my hr-21 lost all channels(sd and hd) as I was flipping through channels. I turned the receiver off and got up this morning and still no channels of any kind were coming in. I went to the menu to check signal strength and the entire receiver completely froze on the view signal strength button. I had to unplug the unit to get it working. When it restarted it was working again. Any ideas as to what the problem might be or how to prevent this from happening again? I have only had this hr-21 since Monday. Thanks in advance for any info!