Fixing boot problem without a Repair disk or working Install DVD

My Windows 7 Professional was working fine until I tried to dual boot the machine with the original Windows 8.1 HDD the machine came with. After muddling through that (and even with much support from the kind people on this forum), I've given up on it because of my own shortcomings.
I have unplugged the SSD Windows 7 was installed on. My machine is back to running reliably booting from Windows 8.1 HDD. Now I would like to unplug the Windows 8.1 HDD (so I can preserve it in good shape to boot from it later) and boot from Windows 7 SSD.
The DVD with Windows 7 ISO is corrupted and won't boot even though it worked fine during original installation. I do not have a repair disk for Windows 7 Professional X64 but have one for Windows 7 X86 which allows me to get to command prompt.
Is there any way I can repair this installation without losing its applications?

carwiz said:

Is your Windows 7 an OEM version or a Retail version? If retail, you can use the key and download a fresh copy of the ISO from Microsoft then burn it to a DVD. If it's an OEM version, you might be able to borrow a DVD from a friend. Microsoft no longer provides the ISOs for OEM versions.

It's retail but I have misplaced the key. I could use some utility to extract it from the SSD once it boots but until then I don't have the key. Downloading a fresh copy from Microsoft requires providing the key upfront. I wish they would allow the download and control piracy by not allowing activation without a valid key. Borrowing could have been a possibility but none of my friends has a Windows 7 Professional X64 DVD.

carwiz said:

Just so you're clear on terminology, you cannot boot from a disk image (ISO) file. The ISO must first be burned to a DVD and the DVD is no longer an ISO file. You cannot simply copy the ISO file to a DVD and boot from it.

I misspoke. The ISO file is probably corrupt because an install disk burned from it gives this attached error at install time. No sure which specific drivers it needs and where can I find them.

Not an installation guru either; I wonder if your DVD drive is on a SATA controller set as RAID.

This machine never was setup for RAID. Windows was installed previously on it using the same DVD.

You can still try changing SATA mode to IDE and see if it will work.

Tried that as well but no success. I will need a good Win 7 Pro install disk to fix it.