XPS 15z l511z - powers on, won't boot

I recently bought a used 15z in somewhat dinged-up shape. The case was a bit dented and the DVD drive was missing, but otherwise it was 100% functional. It came with the i5 and 525gt, 1080p screen, 6BG RAM, which I upgraded to 8GB, and the 750GB HDD, which I replaced with a 120GB SSD. I also upgraded the BIOS to the latest official version, which I think is A12. The battery is the original and keeps a charge for about an hour or so, and the charger is the original OEM part.

After a couple weeks, I took it apart to smooth out some of the dings in the casings, and inadvertently wrecked the LCD. To save money and improve the screen's aesthetics, I bought a new 1366x768 matte-finish screen to replace the original glossy 1080p. It's not an OEM part but claims to be 100% compatible, and the connector seems to match up fine. I've read elsewhere in the forums that the video cable is supposed to be dual-mode and will work with either resolution, as long as the LCD's connector is the right kind.

Once I installed the new screen, the laptop wouldn't start properly. It turns on, but the screen stays blank. It lights up, but there's nothing displayed. The fan comes on after the laptop warms up, the USB ports get power, the keyboard lights up, the battery charges, but there's nothing actually going on. After a minute the keyboard lights fade and won't come back up. Tapping the power button shuts off the laptop immediately.

I've ruled out the RAM and HDD as possible problems by booting with the HDD removed, and swapping in known good RAM. None of that had any effect. It would be a first for me in years of taking apart laptops at home, but my guess was that I must have accidentally shorted the motherboard, so I ordered another, a supposedly 100% working pull from an electronics recycler.

I just now finished swapping the new motherboard in, and there's no change at all. I've searched online for hours but I'm just not sure what the problem is. If I had to guess at it, I'd say it might be the video cable, but without a really solid idea of what's wrong, I'm not sure how much more money I want to throw into it. Counting what I originally paid, plus replacement parts, I'm already out $500. My hope is that someone on here might have run into a similar problem at one time.

--posted from my phone

 

well not all displays are the same...

Can you test the laptop on an external monitor ?

but it seems to me the issue is your display is not compatible or not connected properly

 

Well, I got it working! And yes, thank you, before replacing the motherboard I hooked up an external display. I couldn't get any video out, but I think that's largely due to the 15z only having HDMI for video out, which I believe would require a full, successful boot before working.

I tried a few more things, including cleaning the RAM pins and doing several full CMOS resets, but it turns out the problem was the video cable connector on the back of the LCD. I'd double- and triple-checked it before, but it just wasn't seated properly. How about that?

Everything except the keyboard works now, which is worrying, as the keyboard worked fine before all my issues started. I re-seated the cable several times, but I can't get any input from the keyboard. Hopefully it's the keyboard and not the receptor on the replacement motherboard. I ordered a new one off eBay, so I'll find out when it gets here.

Thanks again for taking the time to try and help.

 

check the keyboard ribbon cable - it may have some damage one of the gold contacts - that's a usual culprit