I have an older PC in which the motherboard is dying. I bought a newer PC and since the HDD is still good on old PC I wanted to install the HDD to the new PC as a 2nd drive. That way i can keep the files and have more room. My question is to make room on old HDD can I delete Windows 10 and not have it mess with the games and files on it?
You can certainly keep any data files- the cleanest way to deal with that is to copy any data off C: to another disk or partition.
If you delete the partitions comprising your Win 10 on that drive (there are more than one!) then any programs installed on that OS will be lost. (Portable programs, of course, can be moved easily).
If you have a lot installed on that consider either
a. Installing them from scratch on your new OS
or
b. automatically transferring them to your new OS using a Laplink program or Easeus Transpro program
(you will need to buy a 1-time use license).
The choice is yours.
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