Yes, we switched off the mains power to the tv.
Model no. is Panasonic TX-28DT2
The tv is about 15 years old.
We get an orange snowy screen and then a picture plus sound (not the right colours), which goes off after a few seconds.
You are saying the problem is down to the age of the TV?
We think it is too much of a coincidence that this has happened when the tv has been switched off, which it normally isn't, we always have it on standby. Could it not be anything else?