Windows 10: After reinstalling Windows 10 on my computer, I can't access my "old OS"

This is a tricky situation, but I'll try my best to explain.For context: I have 2 drives, a 256GB SSD and a 1TB HDD. All of my main files and W10 files were on my SDD and Arch now is on my HDD, leaving a partition of around 400GB where I installed another instance of W10 to try to access my old files, but they are in separate partitions now. My question is, how do I switch the partitions and utilize the correct one?- 128 MB FAT32 And 512GB are the Arch partitions- C: Is where I installed my new Windows instance- D: Is where all of my "old" files, user, and previous windows instance is, a

:)

 

How to reinstall Windows 10 if my computers used the free upgrade from 7 and 8?

Will windows 10 still accept the license keys from 7 and 8 now if I reinstall my computer?

Does Microsoft keep a list of users who upgraded to Win 10 using their 7 and 8 keys so that when users need to reinstall windows 10 the old keys would work?

Do I need to call in Microsoft to ask them to activate my Windows 10 when I give them my win 7 keys?

Both computers are laptops. The windows 7 machine had the serial printed on the back, and I needed to enter that when I upgraded to 10. The windows 8 machine had the serial built in inside its boot system so I didn't need to enter the key when I upgraded to 10, but I did manage to write down the keys using a fetcher program.

 

How to reinstall Windows 10 if my computers used the free upgrade from 7 and 8?

Yes, still work, no need to call, just be sure to have internet access when you start to install 10, I work at pc shop and did this few days ago, used a key of 7 to put clean 10(wasn't used for upgrade).

 

Windows 10 Tweaks

Pressing “Windows+Pause Break” (it’s up there next to scroll lock) opens the “System” Window.

Windows 10: In the new version of Windows, Explorer has a section called Quick Access. This includes your frequent folders and recent files. Explorer defaults to opening this page when you open a new window. If you’d rather open the usual This PC, with links to your drives and library folders, follow these steps:

• Open a new Explorer window.
• Click View in the ribbon.
• Click Options.
• Under General, next to “Open File Explorer to:” choose “This PC.”
• Click OK

credit to Lifehacker.