Panasonic Plasma TH42PX60U loud pop then no picture or sound?

You're damn lucky that you've bought the extended warranty. Yours is a 720p native resolution TV made in 2006. You can tell by the model number.
Anyhow - contact whoever you purchased your extended warranty through. If it was panasonic, call them at 1-800-211-PANA (7262) and ask for the extended warranty department. They will locate a servicer for you through the Panasonic Plasma Concierge Service Locator Group who will set up an appointment through an authorized servicer.
All you will need to do is watch the light blink - there will be a pattern (usually seven or eleven times before it pauses, then repeats). This will help the servicer determine what is wrong. They will come out and attempt to repair the television or replace the board - which will be like getting a new TV. Also, if the TV is wall-mounted, you will have to unmount it before the servicer arrives - they will NOT do it for you.
When you call the number for service - you will need the model number, a description of the problem, the serial number (usually stickered on the right panel of the TV), and your exact date of purchase from your receipt. In order to receive warranty repair - you will need proof of your purchase. Also, they will ask for a prior case number or your first and last name and your zip code to search if you are in their system. If not, they will get the information above and then refer you to another department (either the service locators or the extended warranty division).
If your warranty is purchased from the dealer - you would contact them about the repair. Also - and you may not know this - if you purchased the extended warranty from Panasonic - you are considered a Plasma Concierge member even though you may not have registered or signed up for the card. The card is designed just to make you feel special - but also has a direct number to call so you can get to the front of the call queue and get faster service.
Ask for the exchange program if the servicer has to take your television. If the servicer has a replacement TV available, they will provide it to you until yours is repaired.
Good luck.

There is only one call center for the Plasma TVs in North America - so if you call on Wednesday and get someone named Chris at extension 5712 - I'll be happy to assist you then.