How do I exactly install a 3/4th not so old Sata HD's with data on

Hi forum. I have an OCZ 512GB SSD and 6TB Wesern Digital HD running on Win 7 64bit ultimate custom build. The previous not so old previous sata Hd's being 3tb and 1.5tb I wont to add without losing any data that is on them. I had terrible problems with Acronis software that came with the SSD and gave up on it as were unable to help me. So purchased a new 6tb HD as a 2nd HD to get up and running.

However I now Have a 3tb HD ? formatted as had Win 10 on it a free download - but not happy with it and went back to win 7- which keeps trying to give this back to me as an important update (no mention at all it is a win 10 permanent advert). So as I now know this I don't download it but is easy to do so as mixed in with other (important)updates as is the intention and very sneaky) Plus a 1.5 TB HD also full with video/photos etc.
Now I have installed these two drives (not as a 1st boot of course) - looked at Bios and changed boot sequence a few times.1st lised as UEFI. But having not done this before I thought it would be simple- but so far not seen theses HD's in the Bios or shown on computer. I understand I need to give them drive letter's i.e V for video as Letters F.G.H.I already used up as a portable device i.e card reader. It appears most help assume it is to format new HD's. Which I most definately don't want on the 1.5tb as need data for my video editing software. I recall putting important info onto the 512gb SSD from the 3TB HD and I think I formatted this one to get rid of win 10 as was nowhere as secure as win 7 probably why it was free ( assumption based on Bitdefender reports). I know I can possibly use these as external HD's via extrnal USB. But USB seems stupid. I would like to use the remaing space and keep for storage- I recall the 1.5 tb is actually full.

Sorry if this is a bit long/dis-jointed. Basically am trying to add these two drives without losing any data ? via disk management. I'm sure im missing something silly in getting pc to recognise these drives. etc.
Any one able to put me in the right place and or give an exact plan to follow. Or at least get the 1.5tb HD up and running in system as this has important video data I use in conjunction with my editing software.
Many thanks for any help Robo 5.

Just connect the drives to sata data and power, boot the system.

If you cannot see the drives in windows check the drive management and make sure they are assigned drive letters.

Once you can see the drives in windows go to properties at the root of each drive and give your current (admin) user full access, may need to take ownership, and make sure this is cascaded to all sub folders

If you have issues as one or more of the old drives are still marked active from the previous system installs you can correct this using Partition wizard

Once you are up and running it is probably a good idea to move the required data onto the new drive, temporarily and wipe and reformat the older drives

Hi and welcome to SeveForums,
You can use this to disable upgrading
Upgrade to Windows 10 Update - Enable or Disable in Windows 7 or 8.1 - Windows 10 Forums

I believe Barman pretty much summed up the drive issues :)

Hi,
Most of the problem with the win-10 updates is really just a simple misunderstanding of the update settings that mix up the win-10 recommended updates with real Important updates
As long as the Give me recommended updates the same as important updates is Unchecked they should not cause any I'll effects
Just ignore the Optional section :)

How to remove Windows 10 upgrade updates in Windows 7 and 8 - gHacks Tech News
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