My LG 42PQ3000 is making a clicking noise from the large PCB when power is turned on, there is no picture and the stand by light is going on and off

SOURCE: LG Flat Screen Problem

since when have you experienced the problem? does the tv still turn on or not...?

SOURCE: LG 50PC3D not turning on

Without seeing the unit itself and opening it up/running tests I couldn't tell you exactly what is happening, however I can offer some suggestions as to what it could be.
1) your power supply is bad. That clicking sound is the power relay coming on and going off. 
2) your main board is bad. It handles a lot of your signals for powering on your set. If it's bad, the tv won't turn on correctly as it doesn't recieve all the right signals.
3) your Y or Z boards are bad. These could cause the power supply to go into shutdown if the voltages on these things are too far out of whack. 

Easiest way to tell if you're going to go into your tv is to try to unplug your Y and Z boards and turn it on. If it turns on and stays on chances are one of those two boards are bad. 

Gino Raymone

• 77 Answers
• Posted on Jul 09, 2009

SOURCE: no picture

x and y drivers on the screen ,or shorted power supply

SOURCE: Whenever i go turn the tv on its starts making a clicking noise.

Power Supply board is dead.Replaced the power supply board will solved this problems.Tries websites Shopjimmy.com,Ebay.com to buy a refurbish power supply for the replacement.

SOURCE: Blue Blinking power light

This sounds like a known issue for this TV. LG has a service bullentin #0IVL20090710 regarding this issue.

Try calling LG and let them know about your TV having the know issue and the service bullentin 0IVL20090710. They should fix your TV under a warranty. So be nice when you call to schedule your in home warranty.

LG 800-243-0000

Good luck. I do hope I have helped you.