Your HDCP "handshake" read: "copy protection" is not happening between the TV and the cablebox. This must happen on all digitally connected (HDMI and DVI)devices. Basically this involves the TV exchanging information with the cable box, about their video capablilities and that they are both HDCP compliant. This process will "time out" in your TV, if the devices that need to trade information are not powered up when the TV attempts to exchange info.. If the "handshake" dosen't happen, as you are experiencing, no digital video.

Turning the TV "off" and then "on", solving the problem, tells me that your cable box is not powering up soon enough for the TV to get the HD8300's info. Panny's HDCP implementation does not let an external device reinvoke the HDCP handshake once the TV "times out". Switching inputs to an analog input, and then back to a digital input would acomplish the same results as powering the TV off then on, it reinvokes the handshake.

Unfortunately because you can't specify the device start-up sequence, your only option is to spend a lot of time tweeking your device delay settings (which usually means a very long start-up from off, time), in an attempt to get the cable box to power up before the TV attempts to exchange information, or leaving the cable box on all the time, (which is usually the easier solution).