chromebook 3120 s/n 65jq9b2

There are  a couple of possibilities:

1.  The replacement screen is faulty,

2.  The system suffered more damage than just the broken screen that led to the repair.

See if your supplier will replace the screen.  If the next one does the same, it's likely that possibility 2 holds -- there is damage to the mainboard.

What happened to the original screen that led to the replacement?

I don't know I bought it 2nd hand and it was already damaged, with that said it does not appear to have been mistreated. It looks brand new. So the upgrade should be plug and play? thank you

Did you replace the wiring harness with the new display?  

Yes

It doesn't appear there is a difference between the boards for the touch vs non-touch -- I'd see if your supplier will replace the screen you purchased (or verify that it works correctly, assuming that hasn't been done).  If they tell you it's been tested and was working on shipment, odds are the mainboard needs to be replaced (it supplies the power to the backlight and data signal to the screen).

While it's one check, it'll likely work - from what you've said there IS video going to the display.  It's the backlight that's not working. So the test won't be definitive.

I suspect (confirm when you have it working, positive or negative) that if whatever incident took place to destroy the screen happened with the system powered up, that it took out the backlight power from the mainboard.

Ok, Its hooked up to dell ST2010 monitor, and on the touch screen I still see the same as before (chromebook login screen at a certain angle only, not backlit) while on the external I see a gold and black gecko with a working cursor (no login screen). Does this help or just complicate matters?

do you know if i can hook up an external monitor as a test?

Ok thank you.  

It doesn't help -- it's essentially what you had before.

See if the supplier will verify or replace the screen.  However, I suspect what's really wrong is a bad backlight power circuit - which will mean replacing the mainboard.

Will do thank you for your time