How do I prevent Windows 10 from booting from an old installed drive

I upgraded from Win 7 to Win 10 some time ago, and recently the original hard drive refused to boot, apparently due to boot sector errors. I have installed a new hard drive and loaded Windows 10, and installed all required software. Although I have marked all partitions on both drives as inactive with exception of the windows partition on the new drive, I still receive a blue screen with 2 options for booting (from Disk 0 (the new drive) and also Disk 1. How can I eliminate this? Can I just delete the Windows partition on Disk 1 and this will solve the problem? I would like to keep the old drive and use it for backups.

When I do disconnect the old drive, the computer boots normally.

Welcome to TenForums @LutzF

You should be able to delete the unwanted boot option using msconfig, option 3 in this tutorial shows how to get to msconfig.
https://www.tenforums.com/tutorials/...a.html#option3

Hi Bree

Thanks for the advice. I tried that but the "set as default" option is greyed out - it is already set as the default. This probably means that the default boot drive holds the active system flags. However, I still get the blue screen with boot options on booting. I would like to delete the unwanted windows partition on the old drive - is that now safe to do?

On the boot tab of msconfig, do you show more than one OS listed? If so, highlight the one that you do not want and click delete. Then save changes.

To determine which partitions you can safely delete, we need to see a screenshot of disk management with all of the columns widened so that we can see the data in the columns:
Disk Management - How to Post a Screenshot of

Thanks, that worked - all is ok now.