runningrock :
So I'll just make a fresh install to make things easier. I have precious files in my 2nd partition and I don't have an external hard disk. Files on the 2nd partition will not be harmed right? (unless you format your 2nd partition haha) but there's no case like the hard drive was wiped off when new components are installed right? when i assemble it, turn it on, set up BOOT option then install new windows?
Correct. Just be very, very sure what partition you are interacting with during the install.
There is no 'undo' if you get it wrong.
And for 'precious files'..you really need to have a backup of those.