I'm having the same issue, only today. Its also asking me to check it the HDD connection. Have unplugged/turned off and rebooted SEVERAL times. Could this be a hard drive issue? Seems a little coincidental now that I read your issue too?
So, last night I was able to get the unit working again... after switching on and off several more times - I also went into system settings and pressed "update S/W software OTA" and then everything kick started again (probably coincidence). But then I turned on the TV this morning, got "no signal" message. Unplugged again, rebooted and have now factory reset but now getting the message "media not alive"... at least we can watch TV again. Have a feeling the hard drive has a gone. Maybe time for a new unit... unless anyone can give me tips on how to reset the media?