I am confused, is it that the machine crashes when you load a second drive, but will run with only one attached?

1. Will it run with both drives, if they are the only one attached ("C")
2. Will it run with the original drive as "C" but not the second drive attached as "D"

Could it just be a question of the slave master jumper settings on the drives? You cannot have two master drives.

Are you trying to change the old "C" drive for a new one, and just want to move the data from the old "C"?

What are the make/model/capacity of the drives?

What operating system are you using?

If you give me that info. I can probably help you.

Cheers