Vizio Vx42l Not Turn On

There are several boards in this TV and if any of them fails then your TV will not work correctly. Here is a link that supplies many of the boards at a cut rate price (many were harvested from sets that the screen was broken): http://www.shopjimmy.com/catalogsearch/result/?q=VX42L

If the set doesnt have power supply capacitor problems then this might help understand what is the likely failed board.

If the sets indicator looks like it it's turned "on", and there is sound from the speakers but the screen stays completely black the the inverter boards are likely at fault. you can see that there is actually video on the screen if you put a bright flashlight against the screen in a very dark room.

If every thing is the same as above except the screen lights up slightly, then the T-Con board is likely bad.

If the set doesn't have audio when it turns on, and you cannot turn it back "off" then it's likely the "main" board (or if it never turns "on").

Of course there is a possibility that the "power" board is the cause since it controls all the boards.

remove the back and check for capacitors on the power supply that has the top puffed up slightly. If you find any, replace them. These parts (capacitors) are available at places like Radio Shack. you can either replace them yourself, or take the power supply board and the capacitors to a local TV shop and they will likely charge $20 to replace them for you. The power supply is the module that the AC cord plugs into, and the value of the capacitors is printed on the side. Normally the bad ones are rated at 10vdc-16vdc and they could be 1000 to 2200 microfarads. These capacitors will look like a cylinder with a silver top. Google bad capacitors on LCD HDTV and you will see massive amounts of data.