Windows 7: Windows won't load after HD install

I loaded a sata drive in an empty slot (its an old drive out of my prior computer which has stuff on it that I want to get), hooked it up and started the computer and now it won't load windows, its not the bootable drive either, the windows logo shows up and it just sits there, granted I didn't wait 20mins or something but why would it stall.

I did a hard power off and tried to launch safe mode startup repair and nothing, the green bar just keeps moving across but nothing ever loads? or is it supposed to take forever

Should I just take the drive out and get an external enclosure like I originally planned or have I now screwed up the main drive and windows?

I would suggest getting an external enclosure as you originally planned. It sounds like the boot partition may be damaged on that drive.

You could also try going through the steps for Troubleshooting Windows 7 Failure to Boot.

thanks, I got the drive out and the startup repair worked so the computer is fine, just will get an ex enclosure. I don't understand though why even if the boot part is bad why does that matter since it was a secondary HD and not the boot drive

It depends on how the system scans for bootable drives.
I suspect that, in this case, it found something bootable on the old drive and that stopped things.
Removing the drive and running Startup Repair fixed the problem with your OS - but wasn't capable of fixing it on the old drive.

A USB enclosure is the way to go - but make sure that the system doesn't attempt to boot from it if it's plugged in when you boot.