LG 42PX 4R - will not power up, no red standby light, power cable is fine, checked on another appliance. Any ideas?

Have you checked the outlet to see if it has power?? If not, check the circuit breaker for the outlet. Otherwise make sure all the connections on the P/S board are correct and that they are all connected.

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit stage inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. Viewing it in "Mosaic" or "Magazine" will make surf easy.
http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given. Surf the site with patience.

I came across this in a manual
-Without CableCARDTM : Illuminates red in
standby mode, Illuminates green when the
TV is turned on.
-Inserting the CableCARDTM : Illuminates
orange in standby mode, Illuminates green
when the TV is turned on....
You might want to check your cable card. It seems to mimic your problem. Try taking the card out and gently clean, with a dry cloth, the contacts/strip. Then take some "canned air" and blow out the card socket from the side to dislodge any accumulated debris.

This just happened to me. I unplugged the power cable from the set, plugged it back in, and it worked just fine.

This is a power supply fault, the only solution is to put it into a dealer for repair.

1 It appears that connecting cable is faulty. Normally when you connect and push the power switch the standby light should lit. Try the cable on another appliance and see its function. Also switch on the TV and try to switch it on with your remote control.

bad main pcb

Unplug the TV for maybe 10 minutes, then turn it on. Sometimes these units simply need to recycle. If that doesn't work, you've likely got serious problems.

44 inch lg dlp hdtv no picture or sound press power button standby light turns yellow and then back to red