Cannot install DCS1 release version over DCS2 Alpha on Win10

Hello

I cannot install DCS 1.5 release over DCS 2.1 Alpha, the installation grinds to a halt somewhere when it's copying from existing DCS2 installation, it appears that the process simply freezes. After trying to do something the Operating System also freezes requiring a hard reset.

OS is Windows 10 Enterprise Anniversary Update

EDIT1:

It appears that the updater is able to continue where it left off, so I can at least slowly get to the end, I did 3 runs, the first run was 3GB, then 300 MB, then another 2.5GB, ...

I'm afraid if the updater is properly detecting the files where were interrupted in the middle, so it's redoing those when continuing, if any, so I hope it's not checking just name or size (size can be reserved/preallocated too, depends on program design)

Each time I have to do a hard reboot, which isn't healthy on the OS, background image already got screwed up, but that's okay, this is the first serious Win10 install ever, so it would be too good to be true if it would stick for long ... i've already done a few mistakes with the OS modification (miniscule gui/usability not critical but very annoying) so I have to reinstall and redo my Win10 in a few months anyway, probably before I put DCS 2.5 on, that's a major milestone, will go extra mile to make it really fresh install of that. I can do that when I don't use Win10 for anything other than DCS currently, otherwise I couldn't just play around and reinstall like cookies hehe.

EDIT2:

There's not much to clarify, I have DCS2 installed, and I wanted to install DCS1 for caucus too. Since it's a separate install out of the box, there's nothing I needed to do other than to run the installer, put it into it's own folder, and wait until it finished.

I Had both on Win7 in the past many times.

Edit: It appears that the problem is quite random.

This time it only managed to do 63 MB. But also the OS doesn't seem to completely freeze, it just keeps working super slow, keeps getting slower. Oh I don't like the sound of these clues ...

Edit2:

I ran quick test in WesternDigital Data Lifeguard Diagnostics and it passes ok. Smart is also "good". But it's an old HDD, 41762 power on hours.

Before the OS freezes, first the DCS Updater stops transferring, and it's CPU utilization falls to zero, but the OS displays a busy icon, if I keep clicking, then OS freezes as well, I know it does it since the first time I was downstairs, so it was sitting like this for very long, probably an hour, the screen was sleeping when I got back, it didn't wake the screen up.

It has gone through after 6 attempts.

Unfortunately I didn't save the logs of the previous hard reset before the next attempt.

Hard Drive seems fine, so I'm suspecting maybe it has clashed with the fact that I have some files modified in the DCS 2 install, a few scripts and livery textures.