Hello. It's a tough one as I haven't really messed with Quadro cards before and the M15x can be a little temperamental. It is possible that the vBIOS is causing the issue. The M15x has no integrated graphics so fact that is does boot with an image means that the card is somewhat working. 

Have you removed the old 260M driver using DDU first? Could be an idea just to rule out a driver conflict. 

The M15x uses a light code for errors rather than the beep codes so the beeping is weird. How many beeps to you get?

Thank you for the quick reply. So I've just did that. Instead of reinstalling the GTX 260M I've just pulled the SSD and installed it on another machine to DDU all the existing drivers. Popped the SSD out and back in the Alienware and same issue. After the Windows 10 loading logo the system is still running but it's just a white or black screen and a 2second single beep.
I think I've read here only Dell/Clevo VBIOS MXM cards work. Is that true ? If so is it safe/possible flashing the HP VBIOS to a Dell one ? But I guess I'm gonna have to do that via an eeprom programmer right ? I like this machine and I'd like to upgrade it with this card that's just sitting around so if this route is possible I wouldn't mind trying it.

It should be safe enough to flash a Dell or Clevo vBIOS but flashes are never 100% safe. Yes you will have to use an Eeprom programmer unless you can find another laptop that the card works in and then you can use NVFlash. I have an programmer but I've never actually used it. 

This is all assuming that it's the vBIOS that's causing the issue. There is a good chance that it is but it's hard to say for sure. 

I made a bootable USB Stick with NVFlash and picked up the Dell vBIOS for the K5100M from TPU. I booted from the USB and tried flashing the GPU vBIOS with the Dell version but no success. Well It does say flash successful but the vBIOS it loads looks like the original the card had? This is confusing. See the attached photos below. Anything I'm missing or doing wrong ?

I'd like to note that other than the GPU swap yes the laptop is fully functional with no issues whatsoever (with the original gtx 260m).

I'd like to also note that one time I heard a Windows 10 notification sound when I booted up with the K5100M and the screen remains black or white like whenever I turn on the machine with this card installed. Plugging in an external monitor gives no signal. Should I reinstall the 260M and check if the bios is up to date ? This is basic I know but I don't think that's the issue here.

I think it says that it's the same version because you had already pressed 'y' to change the Subsystem ID. It's risky doing this but I've done it before without having an issue. Usually you need to flash a vBIOS with the same Subsystem ID. If it successfully overrides then you can try other vBIOS' that have the same ID as the new one. 

I've never flashed using the technique you tried above but it seems to be working. 

Making sure the system BIOS is up to date is a good idea, they often increase compatibility with later BIOS versions but like I said before, I have no experience with Quadro cards and they can be a little different to GeForce cards. It could just be that this card isn't fully compatible with the M15x no matter what vBIOS you try. 

It looks like there is only 1 Dell vBIOS for that card. Fingers crossed it works for you

Yes that is unfortunate. I did manage to flash the Dell vBIOS but it's not working with the M15x. I appreciate all the help and suggestions. Thank you.

That's a shame. I'll ask around and see if there are any other ways to get it to work.

You are sure that the card was working in the HP laptop?

Yes I'm sure it's working last I checked. I know it's risky but I did try to flash the 2 other vBIOSes from TPU (the HP versions) one of which gave me signal straight to the external monitor (I believe that was the non UEFI version). But same as all vBIOSes I've tried, it didn't go past the Windows 10 loading screen.

One issue though I'm afraid I no longer have the original vBIOS of the card. It's the 80.04.AE.00.04. I didn't find it online anywhere except in the techinferno.com forums but links are all dead. The guy with the same card and same vBIOS had more or less the same issue as me when he first installed it in his Clevo laptop and had apparently successfully made it work after a vBIOS flash. He posted the working vBIOS as well as the original vBIOS but as I said links are down.

Well if nothing works worst case I'll just order a 970M 6GB and install it in there. They're not that expensive these days (150$ doesn't sound too bad to revive an M15x). Those Clevo variants should work no problem yes ? It should be able to boot to Windows with the Microsoft basic display driver. All I need is installing the modified nvidia drivers is that correct ?