Windows 7: How do I make a Win7 hard drive NOT bootable?

I am adding an additional used hard drive to my new system. This disk has Windows 7-32 on it that I plan to eventually reformat. After installing this disk in my new Windows 7-64 PC it starts as a dual boot. "Windows 7" or "Windows 7". Neither will boot. Unplugging that drive, it starts fine. I'd rather not format this drive yet unless I have to. What are my options?

So if both drives attached you see a boot menu with 2 boot options?
If you detach one of them it boot fine (from the other one).

Attach the old none working disk only. Or attach both.
Boot from Windows 7 system repair disk or Windows 7 install dvd. Then do Partition - Mark as Inactive
Mark all volumes inactive on NON BOOTING disk only! To find correct volumes.... check the size of volume. Does it boot now?

Both are sata drives? Can you swap the sata cables, so working one is tried first

Yes, both drives (2 Win7s) I had 2 boot options, one drive, one option. Both SATA.

<<Then do Partition - Mark as Inactive Mark all volumes inactive on NON BOOTING disk only!>>
This worked. However it said "Volume was already inactive" but I don't think it was. Upon rebooting I again had two options, I chose the first. It went to a 'partition repair' or something like that then back to the dual boot screen. Both options said "Windows 7 (repaired)" . Chose the 1st again and all is well. I still get dual boot but just choose the 1st.

I always like to ask for a snipping tool picture of your Disk Management window. Then we can tell what is actually going on. After you take the picture, attach using the paperclip.

Here is where I stand now (See attached). I still get dual boot screen and both options say "Windows 7 (Recovered)" but once I get in, it seems to be running normally. I expect to be reformatting Disk1 (J: and K soon.

As suggested mark Disk 1 SysReservd partition Inactive: Partition - Mark as Inactive - Windows 7 Forums

Then mark DIsk0 SysReserved partition Active: Mark Partition Active. Reboot into BIOS setup to make sure DIsk0 is set first HD to boot..

Now boot into the Windows 7 DVD System Recovery Options or the System Repair Disk to run Startup Repair - Run 3 Separate Times until Windows 7 on C starts and Disk0 SysReserved partition holds the System Active flags.

You can now delete and format the partitions on Disk1, repartition as desired in Disk Mgmt. If a ghost boot listing appears, delete it in msconfig>Boot tab.

If Disk1 interferes with the Repairs, unplug it and start over.

If you marked all volumes inactive on NON BOOTING disk... you can't boot from it. So you boot from other disk as always. You should still have ONE boot option. After "startup repair" it can discover other bootable Windows 7/vista OS's and add it to boot menu.

If you select the 2nd in dual boot list... does it boot as well? Wanna keep it?

Please post screenshot of "disk management".

I ended up going to msconfig and just deleting the 2nd boot option. That disk will be reformatted soon anyway.

You only hid the problem, which is that the boot files are on a disk you no longer intend to use and plan to format. You won't even be able to format DIsk 1 while it holds the System flag, and if you force it then it will cause C to become unbootable.

You must move the System flag from Disk1 to System Reserved on Disk0 following the steps I gave you. Why would you ignore steps which I typed out to do something we've helped countless thousands of users do here successfully?

I'm trying to do that but ran into a problem (See attached). I want to make vol3/Disk0 inactive but it doesn't have a letter that I need to select. It is also marked as 'SYSTEM'. Is it possible the system flag is on disk1 and the OS on disk0? I want to use disk0 for both (I: and C and reformat disk1