Picture Come and Goes

I own a 4 year old Mitsubishi WS55511 HDTV.  My problem occurs intermittently.  The picture will flicker off for a few seconds, 5-10, then flicker back on for a few seconds, then off, then on, etc.  The sound will always be on.  This problem occurs randomly....days will go by with no problem and then the flickering will start again.  When the flickering picture occurs I get a message on the screen that says, "SAT 1080i, Standard.      Check connections or power. The connections for RGBHV or YprPb may be invalid."    Sometimes, along with the picture on and off problem, another problem develops that I can only turn on or off the set at the set itself, not with the remote.  These problems have been happening for the last 30 days or so.  Any suggestions you can give regarding this problem are greatly appreciated!  Thank you very much.