Desktop PC was previously my W8.1 computer.
I had backed up all my data as at 31 Dec 2015 in preparation to upgrade to W10.
I had 3 separate 2TB hard drives in this PC with backups to internal second and third drives.
All three hard drives were partitioned into two 1TB partitions.
All three 2TB hard drives are Samsung HD204UI 2TB models (now all out of warranty period)
This Deshtop PC was then updated to W10 on 4 Jan 2016 (after creating a new restore date in W8.1).
Luckily I also backed up to separate external hard drives.
Now a W10 Desktop PC it died during Critical Update 18 Jan 2016 for "unspecified" error. W10 desktop PC just stopped during this update with following problems;
1. no BSoD - just totally blank dark screen.
2. unable to switch off, or reset or power off via PC.
3. had to turn off power supply after 6 hours (of hoping something will happen).
4. unable to restart PC - BIOS loads - then W10 logo appears (Flashes on) - then PC just hangs. At least it now resets to restart.
5. unable to start into safe mode. or any other variations of safe mode.
6. After some 10+ restarts attempts - now get option to restore to an earlier date - my last W10 restore date was 15 Jan 2016.
7. Restore failed for 15 Jan 2015 due to "unspecified error". Tried again 3 times with same result.
8. Restore failed for same reason on several earlier restore dates ( I make a new one each fortnight).
9. Nothing in Microsoft's Windows 10 helpsite helped.
10. Took it to my local long term "Microsoft Most Valuable Professional (MVP)" repairer, who found the following problems;
A. Master Hard Drive 2TB (previously 2 @ 1 TB partitions) - only C drive (1TB) able to be accessed. Drive has been corrupted - he is still working to recover my Windows (old) files for me.
the other 1TB "D" drive is now not there. ie shows as only total of 1TB available.
B Second hard drive (previously 2 @ 1 TB partitions) - "E" drive (one 1TB partition) is now "not accessible - access is denied". the other 1TB "F" drive is now not there. ie shows as only 1TB available.
C Third hard drive (previously 2 @ 1 TB partitions) - "G" drive (one 1TB partition) is now "not accessible - access is denied". the other 1TB "H" drive is now not there. ie shows as only 1TB available.
Has anyone had similar problem with W10 recent upgrades or updates?
Why would hard drives reduce from 2TB down to total of 1TB?
Why would update effect other internal hard drives other that C drive?
Help

Yes I am now using old W7 Home Premium desktop PC.
My W7 "Backup" PC System Profile (as at 20 Jan 2016)
Computer type: PC/DesktopSystem
Manufacturer: custom
Model Number: custom
OS: W7 Home Premium
System Type: 64 Bit O/S
CPU: Intel Pentium D 3.40 GHz 3.40 GHz
Motherboard: GIGABYTE 8I945PLGE-RH
Memory: 3.25GB (4GB)
Windows Experience Index 4.6