Question about Laptop motherboards

So I have a Toshiba Qosmio X505-Q887 laptop that needed a new motherboard. The video card was shot and my attempt at performing a reflow failed.
When I found the board on EBay I compared the model number and at first glance it looked like the one I needed.
The model number is                               A00005090
But the one I bought was actually   A00005040
I didn’t notice the last two digits were different until I received it but they look completely identical
In every way so I went ahead and installed it.
Unfortunately I still had a black screen but the VGA output was working fine with an external monitor.
I replaced the entire monitor with an identical known good one from another Toshiba X505 –Q887 but still have no video.
I have updated the bios
Updated the video driver
Installed two new memory modules but still not even the slightest bit of light emanates from the computer monitor.
My question is this,
Could using a MB with a slightly different model number have an effect on this?
I can access window through the external monitor, and it does show up in the device manager and indicates that it is working properly.
The function keys work but have no effect on this problem.
My thought is that the monitor is really supposed to be paired with the A00005090
Board but if that’s the case then why does everything else work.

thanks in advance
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Laptops usually have a switch of some sort that tells the system whether the lid is closed or open. When the lid is closed that would turn off the internal display. Maybe that switch is broken, not connected to the mainboard, or blocked by something so it is always in the "off" position.

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Dr. KlahnPrincipal Software EngineerCommented:
It is certainly possible that the motherboard model is the issue.  If the motherboard you got is for a laptop that uses a different display module, the results would be what you're describing -- no laptop display, but the VGA/video output and all other features work properly, at least until Windows starts.  After that the behavior would be a guess at best.

Unfortunately I couldn't find references to either board online, so this is speculation.  I suggest following rindi's comments above, and investigate the lid switch.  Chase the cabling all the way back to the motherboard and check the lines there with a DVM, as it may be the cabling that is broken and not the switch.
TplayerAuthor Commented:
I would never have thought of that. Problem solved.
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Displays / Monitors

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