I have a Panasonic Model PT-50LC13 flat TV. Was working when got it brought it home, it is used and now when I go to turn it on --- we get a green light then a flash of 5 yellows blinks then no light for 5 seconds then flash of 5 yellow blinks.

Hi,
This tv has 3 indicator lights on front, Power, Lamp and Temp
I assume Temp light is blinking 5 times after every 5 seconds, if that is correct then it is problem of clogged air filter located in light engine that need to be cleaned.
Below is an image of light engine and air filters locations are marked with red circle, it is job of professional to fix this issue because complete light engine need to be take out from tv cabinet.
Hope these info will help you, let me know if you have additional question or need service manual copy if you want to repair tv by yourself.
Thanks.