Cannot boot Win 10 on GPT drive

#1
Old configuration: Two MBR hdd, one with Win7 Ult x64, other with XP, separate boot partition. Win7 set in BCD as default boot. Asrock mobo with UEFI bios booting in legacy mode.

Next, added new large hdd formatted as GPT with UEFI and MSR partitions. Installed Win7 Pro + SP1 from DVD in UEFI mode, with other two hdd unplugged. Win 7 boots fine using UEFI boot to Windows Boot Mgr.

Reconnected other hdd and added 7 Pro as a third boot option to the BCD on the MBR boot drive, pointing to winload.exe on the GPT partition. No problem booting the GPT partition from the legacy boot.

In single hdd configuration, upgraded 7 Pro to Windows 10. 10 boots fine via WBM. Reconnected other hdd, and 10 still boots fine from WBM. Set boot drive back to legacy MBR. Deleted 7 Pro entry and added new entry for 10 Pro, again pointing to winload.exe on the GPT partition.

Although 7 Pro could boot fine from the GPT disk using the entry in the legacy BCD, Win 10 will not boot. I'm getting error 0xc0000428, "...cannot verify digital signature of winload.exe" Secure boot is disabled, so I don't know why I'm getting this. I can boot 10 fine using the BIOS boot menu to select WBM, or let it default to the legacy boot to start Win 7. So I can either add Win 7 to the boot menu used by WBM (how?), get 10 to boot from the legacy BCD (how?) or use the BIOS boot menu.

Please advise.
 

Terry60

Knows where his towel is.
Staff member
#2
You can't load a newer Winload from an older bootmgr.
Normally the advice would be to add W7 to W10's BCD, but in this case that's impossible because of the UEFI/GPT - MBR clash.
Drag a copy of W10's bootmgr across to the W7 HDD (rename the smaller W7 version first to avoid it being replace in case you want to go back at some future point.)
 
#3
So, the Win 7 on the MBR disk cannot be added to the Win 10 boot menu because Win 10 is booting in UEFI mode, and therefore can't start 7, is that correct? But when I first installed 7 Pro on the GPT disk, it would boot just fine. Why can't the 7 Ult on the MBR disk be started this way?

If I copy the bootmgr from the root of the Win 10 partition to the default MBR boot partition, will the existing BCD work with it?
 

Terry60

Knows where his towel is.
Staff member
#4
1) MBR BCD can boot GPT systems, but not vice-versa
W10 ~> 8.1 ~> 8 ~> 7 ~> Vista (boot backward compatible, will work)
W10 <~ 8.1 <~ 8 <~ 7 <~ Vista (not forward compatible, won't boot)
2) Yes, the BCD format hasn't changed, just the bootmgr module.
 
#5
I copied the new bootmgr to the MBR boot drive. Now I can start 10 from the boot options. Thanks! I was expecting the new light-blue GUI multi-boot screen, like Win 8/10, but it was the same B&W character screen as the old bootmgr. Why?
 

Terry60

Knows where his towel is.
Staff member
#6
It's not just bootmgr which affects that.
 

mqudsi

Mostly Harmless
Staff member
#7
Use EasyBCD 2.3 and enable the metro bootloader option.