I thought that I had posted a note awhile back but apparently didn't finish it.
Unfortunately your suggestion to use sfc didn't solve the problem (i.e. "The digital signature of the Windows 7 'winload.efi' couldn't be verified)". I did some checking and "FC" says Windows\System32\winload.efi and the backup Windows\System32\Boot\winload.efi are identical. That makes me wonder if error message doesn't completely describe the problem.
Unfortunately during some experimentation I made matters
worse. I used Visual BCD Editor. After saving copy of the store that loaded
Windows 10, I imported a previously
exported store that used to load Windows 7. Unfortunately I closed Visual BCD Editor
while looking at it. Now every time I
try to boot, it tries to boot Windows 7 and gives the "winload.efi can't be verified"
error so I can no longer boot at all. Windows 7 is the only system available.
I have tried to use the Windows 10 Enterprise install disk to repair the computer without success. I tried to use the repair's command prompt option. (The default "disk" is now X.) It allows me to see the C (windows 10) and D (windows 7) partitions. I have tried several things all at the "X:\Sources prompt:"
bcdboot c:\windows /s x:
It gives the message "BFSVC Error: Failed to set element application device. Status = [c000000bb]"
gives the message "The boot configuration data store could not be opened. The requested system device cannot be found."
bcdedit /import c:\BCD_Backup_21Sep2016
where the file is the exported file that loaded Win 10. It results in the error message "The store import operation has failed. The requested system device cannot be found."
sfc /scannow /offbootdir=X:\ /offwindir=D:\windows
results in "There is a system repair pending which requires reboot to complete. Restart Windows and run sfc again." But the same message appears after starting over with the install DVD.
I have also tried to reinstall both Win 7 and Win 10 without cleaning the disk. In either case, when the question "Where do you want to install Windows?", no matter which partition is picked, it says "Windows can't be installed on drive 0 partition n (Show details)" The details: "Windows cannot be installed to this disk. The selected disk is of the GPT partition style." That is extremely strange as when the same DVRs were used to install the OS's, they both insisted on a GPT disk.
Are there any more suggestions that would allow me to salvage the existing Win 10 or Win 7 systems? Or should I just clean the disk and then try to install the systems again?