"No Signal Message" on TV During Turn-On

One of my TVs, upon turn on, has started showing a message on the screen  in a turquoise background: "HDMI 1" No Signal--retighten cables..."  I notice that during this message the set box light remains solid. Usually in about 10 seconds my TV programs come on. Or, I turn the TV off and on and programs come on.  Cables are tight  As a side note, I recognize that same "No Signal Message" when reboots or upgrades begin on my TVs.  The TV reboots always start with the "no signal" message and the DVR-cable box and set boxes blink until that message goes away and the reboot continues.    But back to this issue, I don't understand why one of my HDTV's---a one year old great playiing Sony---has started to come on with  the "No Signal" message.  Has that happened on any of your TVs, and if so, what's the cause and how did you fix it?  Thanks for putting up with this long message.