LG 47LV5500 TV. No image at all, replaced all three boards, no luck!

So, I have an LG 47LV5500 TV

(http://www.lg.com/us/support-product/lg-...)

This TV was broken when I got it (a "specimen" given to me by a friend to play with).

When I powered the TV on, I see that the white light at the bottom right corner is on but that's it. No image, no sound. Nothing came up. Not even the LG logo. The remotes that came with the TV didn't work either, save for turning the TV on and off.

If I press any other button on the remote nothing comes up.

By the way these remotes can turn on and off other TVs in the same room, but that's probably not relevant.

For exercise purposes, I decided to get all three replacement boards (power, main and T-Con), all brand new, I replaced the power board (same problem persist), then I replaced the main board. And then something happens.

The LG logo pops up with what looks like a clock icon but with four dashes like this

--:--

So, I thought, I need to reload the firmware at this point. I took a break and went on with my life. The next day I tried to turn on this TV on hoping to get that logo up again. I never found out how to reload the firmware so I tried using a newly formatted USB flash drive, create a folder in it called LG_DTV and plug it in as if I am trying to upgrade the firmware. At this point suddenly the image turns off!

So I unplug everything, power cord and USB. Then I tried to turn the TV on again, hoping to see that LG Logo. Nope. Nothing. No image shows up. I am back to square one. I am so bummed.

I don't think the USB has anything to do with the disappearance of the image, but who knows...

One thing to mention, the main board does have an on/off switch on it. It's one of those microswitches, does long pressing this microswitch reset the board to factory setting?

Please help. Let me know if you want pictures, videos, etc.

Thanks,

L