15" Mid-2012 MBP - Windows wont boot with another drive in the laptop

[JDLang76]

I installed Win7 on a 3G SSD in the optical bay using an adapter. Then i installed the correct Bootcamp drivers. Then I updated to Win10 from within Win7. Everything goes great. Win10 has all functionality, no crashes, and boots every time. THEN. I put my Mac OS/Linux SSD back in the main drive bay and POOF, Win10 no longer boots. Take it out? Win10 boots again. I use this exact drive config in a 13" Mid-2012 and a 17" Late-2011 so I'm confused why there's an issue here. The only difference is I did NOT use Bootcamp/Win7 on those other two. With them, I installed Win 10/11 straight away. For some reason, the intel hd driver crashes Win10/11 on this 15" Mid-2012 unless I start with 7. Since Bootcamp is the only difference, I'm assuming therein lies my problem? Any help would be appreciated.

 

[DeltaMac]

Is there any change if you swap drives -- Mac OS/Linux in optical bay adapter, and Windows drive in main drive bay?

With both drives in place, do you see the Windows drive in the Option-boot manager screen?
When you boot to macOS - do you see the Windows drive in System Preferences/Startup Disk, as a choice?

If you have both drives in place, and boot to macOS, change Startup Disk to select the Windows drive as the default startup disk. Then try to boot as a simple restart, and finally, shut down (so system power is OFF, then press and release the power button. The Windows boot drive is set as the default (double-check to make sure Windows is set as default) Does Windows boot from a restart, or from completely off?
If not, what does happen? Does it boot at all? Which system finally boots?
Have you tried swapping out SATA cables? The SATA cables are known to "flake out" and might cause really odd boot issues, or just fail to boot at all.

 

[JDLang76]

Is there any change if you swap drives -- Mac OS/Linux in optical bay adapter, and Windows drive in main drive bay?

With both drives in place, do you see the Windows drive in the Option-boot manager screen?
When you boot to macOS - do you see the Windows drive in System Preferences/Startup Disk, as a choice?

If you have both drives in place, and boot to macOS, change Startup Disk to select the Windows drive as the default startup disk. Then try to boot as a simple restart, and finally, shut down (so system power is OFF, then press and release the power button. The Windows boot drive is set as the default (double-check to make sure Windows is set as default) Does Windows boot from a restart, or from completely off?
If not, what does happen? Does it boot at all? Which system finally boots?
Have you tried swapping out SATA cables? The SATA cables are known to "flake out" and might cause really odd boot issues, or just fail to boot at all.

Cant swap drives cuz 6G drives dont work in the optical bay of this model.

Yes, Windows is in System preferences start up menu. If I restart using the system preferences menu, it does the exact same thing.

All I get is a blinking cursor in the upper left-hand corner of a dark gray screen. It stays that way indefinitely until I hard shut off the computer.

I really don't think it's a sata cable

 

[JDLang76]

Just realized something. Using Bootcamp creates a boot menu option titled Windows whereas instaklling fresh creates an EFI Boot. I made a W10 bootcamp USB and that USB showed Windows AND EFI Boot options. Selecting Windows generated that same blinking cursor problem. It has something to do with "Windows" vs "EFI Boot."

 

[DeltaMac]

But, you say that if you pull the drive out of the main slot, leaving the Windows drive in place, it will then boot Windows without complaint ? Am I correct on that?

You say that it won't use a 6G SATA drive in the optical bay -- and you have to use a 3G drive.
What model of SSD are you using in that optical bay?
Anything that I see shows that 2012 model has 6G SATA on both bays. But, you are the user, and are certain about that... so I have no anecdotal info myself, except to know that the negotiated speed on SATA bus is finicky on some Macs.
Have you tried a second 3G SSD, so there is no difference in the negotiated speed on both drives, so both will be 3G. I'm not very sure that will actually help, but might be worth the try.

But, before you go into THAT...
Your last post also triggered a new idea in my mind...
You could try a "repair install" for boot issues.

Windows boot issues troubleshooting - Windows Client

Learn to troubleshoot when Windows can't boot. This article includes advanced troubleshooting techniques intended for use by support agents and IT professionals.

docs.microsoft.com

Scroll down to "Boot Loader Phase", and you will see that one of the symptoms is "black screen except for a blinking cursor.
Good luck!

 

[JDLang76]

But, you say that if you pull the drive out of the main slot, leaving the Windows drive in place, it will then boot Windows without complaint ? Am I correct on that?

You say that it won't use a 6G SATA drive in the optical bay -- and you have to use a 3G drive.
What model of SSD are you using in that optical bay?
Anything that I see shows that 2012 model has 6G SATA on both bays. But, you are the user, and are certain about that... so I have no anecdotal info myself, except to know that the negotiated speed on SATA bus is finicky on some Macs.
Have you tried a second 3G SSD, so there is no difference in the negotiated speed on both drives, so both will be 3G. I'm not very sure that will actually help, but might be worth the try.

But, before you go into THAT...
Your last post also triggered a new idea in my mind...
You could try a "repair install" for boot issues.

Windows boot issues troubleshooting - Windows Client

Learn to troubleshoot when Windows can't boot. This article includes advanced troubleshooting techniques intended for use by support agents and IT professionals.

docs.microsoft.com

Scroll down to "Boot Loader Phase", and you will see that one of the symptoms is "black screen except for a blinking cursor.
Good luck!

Nothing. Thanks though. I think I am going to abandon trying to get the non-EFI option to boot and redirect my efforts to fixing the graphics issue in Windows 10. I'm hoping that might be easier