Precision M6700 posts normally but doesn't boot after CMOS reset

Hello,

I'm facing the weirdest issue I ever had on computers.

I was testing a Quadro K2100M on my Precision M6700 and it worked without any issues with Optimus enabled. So, just to confirm, I tried to disable Optimus and see if that's going to work. It didn't, probably because K2100M doesn't seem to have LVDs connections (yeah, that got me by surprise too). Screen was lit, but it was black and I could see the screen if I plug it in an external monitor.

In this situation, I had 2 options: removing EVERY HEATSINK, GPU FAN AND GPU ITSELF and then boot without it to activate Optimus again automatically or doing a CMOS reset. Since last one was a lot easier, that was my choice.

Laptop posted normally, warning about time and date settings, as expected. So I just fixed that and changed Legacy to UEFI boot. Saved, reset and I noticed that screen was black for more time than normal, so I turned laptop off. Trying to boot again... same issue.

At first I thought CMOS reset just destroyed UEFI settings, so I got a Windows 10 installation flash drive that I had here and I was planning to fix boot partitions from there. For my surprise, it didn't boot either.

I could access F12 boot menu without any issues and there are no problems on detecting HDDs/SSDs/flash drives at all. It just went to black screen after selecting boot device.

After that, these are what I tried:
-CMOS reset (again).
-NVRAM reset (taking off CMOS battery and pressing power button for 30 seconds unplugged). NVRAM reset seemed to work, since I lost UEFI boot settings.
-Change GPU (tried with GTX 970M and K3000M and no GPU at all).
-Change memory sticks to different slots and even using different ram sticks.
-Change CPU (yeah, even that. Laptop had a i7 3840QM and I tried with i7 3610QM that I had in another computer).
-Boot with legacy drives (an HDD and a flash drive that I have Windows to Go installed).
-Activate secure boot, deactivate "legacy and UEFI" option.

The only situation that was different was on last one. With secure boot activated, Dell logo stays on screen, but it never boots anyway. If I wait long enough (about a minute or so), laptop just resets itself, posts normally and tries to boot again and that's it. Infinite loop.

I also noticed that I can't access "Diagnostics" option on F12 boot menu. It also goes to a black screen.

Do you guys have any clue of what happened? I'm out of ideas and I don't know what to do anymore . If that helps, I have a CH341A Programmer laying around here and I could use it if that would make a difference.

Thanks in advance.

 

This sounds just like what happened when I tried to boot with a Quadro P5000 (with stock vBIOS, not ES vBIOS). It would hang at the Dell logo and not boot any OS that I tried (Windows/Linux/DOS), and if I waited long enough the system would seem to restart but then still be stuck in the same state. In this case the problem was installed by reinstalling my old GPU, though...

Basically... If CMOS reset (after a known-working GPU is installed) doesn't work, I'm flat out of ideas, if it were me I would probably start thinking about motherboard replacement :-\

 

Well... shoot. If you, of all people, have no idea what it is, I guess I'm stuck :T

I found a dumped bios here and I'm willing to try that as last resort. But first, seems like PXE booting is still working, so I'll try to boot from there. If I'm successful, do you think that I will be able to reinstall bios update inside Windows 10 Installation or even Linux (Ubuntu Live)?

 

If you can get a regular-ish Windows environment up and running then you should be able to go through the regular BIOS update procedure.
I think that you can also update the BIOS, from a file stored on a flash drive, right from the F12 boot screen? (Never actually tried this; maybe it is only newer systems that have the option.)

 

Even if it was an option, seems like laptop refuses to boot for anything. Tried PXE boot here and it got stuck with black screen. To confirm that was working, I tried to boot with my M4600 and it worked without any issues. It's really bad that this laptop doesn't have any kind of boot recovery like Precision 7510/7710/newer models.

I tried to read bios chips with programmer and it only shows repetitive hexadecimal codes. I opened the bios dump I got and the pattern is completely different, so it's probably read/write protected. I didn't find much about how to turn off this protection, the only thing I know is that I have to do a Flash Descriptor unlock and this is the only tutorial I found. I have absolutely no idea how to even begin.

So yeah, seems like I need a new mobo or buying bios chips and do some soldering. Since I have no experience about soldering, I'm stuck with a new mobo. $100 on Aliexpress, so yeah. I'll do that, unfortunately.

Thanks for trying to help anyway, dude.