In short: UEFI uses GPT and Legacy BIOS uses MBR. You know what had kept this conversation really short? If you tell us what windows edition exactly was originally pre-installed on the laptop.
Is there any tool that takes in the key and shows which version it applicable for? This couldve solved my problem to begin with. I just hope I dont have to go win8.1 single edition too, hopefully win10 single edition should work.
No idea. I just know from one of the BIOS key extractors that the Windows 10 installed was HOME single language. So I guess the previous windows 8 or 8.1 was single home too.
Windows 7 oem doesn't use oemm but slic2.1 table. Win 10 can't/doesn't use slic2.1 so it will not interfere.
Okay so the problem is fixed. The issue was I was installing normal ISOs of Windows 10 or 8.1, and NOT Single Editions. I downloaded Windows 10 Home SINGLE EDITION from windowisodotnet and during setup it asked for the product key. I entered the product key from my UPGRADED Windows 10 Home Single Edition (that I had from an extractor). It recognized that and everything went smoothly from there. The thing I learned is, the WINDOWS 10 product key that was extracted could be used for a CLEAN install.