Welcome To My Hell

Yeah, I had the same problem.

In a nutshell, if you have any bootable files on the other disc, it will be classified as active, and your multiple hard drives will be bickering about who gets to be C:\.

Of course, if you’re already booted into Windows 7, then you will probably not be seeing the other drive.

So. How do we get it to show up in My Computer?

Head on over to:
Control Panel -> Computer Management -> Disk Management (In Storage)

You should see your IDE drive now. If you don’t see it. Then you have bigger (albeit easy to fix) problems.

Right click on your IDE partition.
Select ‘Change Drive Letter and Paths’.
Click Add.
Verify that radio button: ‘Assign the following drive letter:’ is selected.
Pick a drive letter.
???
Profit.

Enjoy.