Dual boot. Two problems.  

Problem 1 :)

I've successfully installed W10 to dual boot with Vista. It works well but for one irritation, which is that I am asked for my password every time I select and boot to W10. I get that multi-coloured W10 rainbow lock screen ? the one that you click and it then changes to the normal password screen. Once into W10 I can confirm that the OS is still set to NOT require a password (on the netplwiz screen).

So why does it ask for one ?

(A bit more info if its relevant... the Vista install can be considered a normal clean install. The W10 installation was added onto the D partition by restoring a working Acronis W10 image to that partition. The W10 image up to this point was a clean install in its own right on its own HDD. No dual boot. It was configured NOT to require a password and in use it never did. Once that image has been made into a dual boot with Vista it does ask for a password)


Problem 2 :)

Explorer in Vista shows both installations as can be seen. The C and D partitions. Look at this in W10 and the Vista partition doesn't show.



And one partition is missing in W10.

If you look in Disk Management in Win 10 I expect you will see there is no drive letter assigned to the Vista partition.
That would explain why you don't see the Vista partition in File Explorer.

I don't know why it's asking for a password.
You can work through this tutorial by Brink and see if it helps.
Log On User Account Automatically at Windows 8 Startup

David :) I think you have it.

Yes, it seems so. It gets a bit confusing because C is always the active partition in use.

Yes, if you want to see the Vista partition in Win 10 just add a drive letter.
I don't use a drive letter for other OS partitions on a multi-boot PC.
It helps keeping things from mistakenly being placed on the wrong OS partition.