Win10 drive wn't boot because of deleted win7 drive?

[SkogsBacon]

So I have pretty weird situation, I wanted to see if some drivers worked with win7. I need them for school, I tested the drivers and they worked.
Here is the weird part. I booted into the win10 usb stick to format the drive with win7. The drive got deleted and I created a new partition. Then I tried to boot to win10 by restarting the PC. Some kind of error appeared it told be to boot to win7, i pressed enter. And it was not viable to boot to win7. I then disconnected the drive which had previously had win7 on it. And it booted to win10???
I couldn't connect the drive again because something went wrong when i disconnected it. I haven't looked into it so much. This has happend before when I deleted a linux partition on the same drive.
What causes this? When a drive is formatted isn't it supposed to be nothing on it? Please help???

 

[Colif]

so you had win 7 & win 10 on same PC? I assume you had a menu appear at boot each time asking which you wanted to load?

Now you deleted win 7 but that boot manager is still there.

ON win 10, right click start button and choose run...
type MSCONFIG and press enter
choose boot tab
choose Win 10 and make sure its default.
choose Win 7 and remove it if it is in here. This should remove the menu after a restart. You should be able to plug the old hdd in now

 

[SkogsBacon]

so you had win 7 & win 10 on same PC? I assume you had a menu appear at boot each time asking which you wanted to load?

Now you deleted win 7 but that boot manager is still there.

ON win 10, right click start button and choose run...
type MSCONFIG and press enter
choose boot tab
choose Win 10 and make sure its default.
choose Win 7 and remove it if it is in here. This should remove the menu after a restart. You should be able to plug the old hdd in now

Thanks, going to give it a shot!