Hello everyone. It's a long story and I'll try to explain my problem in detail. So, please bear with me if it's long.
First of all, the OS I was using was Windows 7 ultimate, 64 bit.
I had four partitions on my 1TB hard drive and I wanted another one to install Ubuntu. So, I googled a bit and realised Windows 7 itself can create new partitions without losing data unlike XP. The method was shrinking a volume by a specific amount so it turns into unallocated and a new partition can be created of it.
So, I googled around and saw that windows 7 doesn't allow more than 4 partitions on home, home premium etc but it does on ultimate. So, I decided to go ahead with it. While creating the new partition of 10gb from the unallocated partition, it prompted me this message:
First big mistake when I clicked yes.
It asked me to reboot and I promptly did it. To my shock, I see the OS won't boot and the BIOS got stuck at "Loading New Operating System.."
So, I plugged in my bootable flash drive containing ubuntu and loaded the live cd. At this point, the data was still with me and showed up in the ubuntu file system.
I researched a lot and decided that re-converting dynamic to basic would fix everything (how stupid of me).
A bit of researching and I reached How to non-destructively convert dynamic disks to basic disks | My PKB
Reading the comments, I saw a lot of positives for testDisk, albeit for not so similar issues. So, I went ahead with it (without a backup. Arghh!). Another reboot and now no partitions show up on ubuntu live disc. I panic a bit. That's 700 GB of data gone right there, I thought!
I installed Win 7 on my other disc and frantically start going through recovery tools and try to get my data back. At this point, my new drive's OS showed just a single drive "F" which was inaccessible. I formatted it (another mistake but didn't cost me at all, thankfully). Now, while running EASEUS data recovery, it listed down 4 partitions of the exact same size as my partition sizes before everything got messed up. I googled more and realised these were partitions that got hidden.
I found a tool called MiniTool Partition Wizard (thank god I did!)
Ran a detailed scan on my messed up hard drive and restored all the four partitions. And voila! all my data is back!
Now, I plug out my working OS disk and try to boot my messed up - partially fixed drive and it won't boot and take me straight to "Boot from CD" option. At this point I tried the recovery option reading this: MBR - Restore Windows 7 Master Boot Record
But the OS doesn't show up at all. So, after this long, long, very long story, I'd like to know if there is a way I can get my OS back without losing any data and settings?
I know if I install Win7 on C drive again of my 1Tb disk, it won't mess up with the existing files there and just fix the boot issues. But I'll lose my program files and settings, installed folders etc. (Same thing happened with my other disk, that's why).
Thank you for your patience and I hope this detailed summary of my issue can help out someone who ends up going through this in future.