Please please help!

I have installed Windows 7 Ultimate on same hard drive on D Drive on my laptop and the previous Windows 7 Enterprise which was installed on C Drive is not booting up now.

When I turn on my laptop, I see two Windows 7 on the screen, when I select newer one, it starts, but when I select older one which is Enterprise edition, system won't start and I get the DOS black screen with this error message:

Windows Boot Manager

Windows failed to start. A recent hardware or software change might be the cause. To fix the problem:

1. Insert your Windows installation disc and restart your computer.
2. Choose your language settings, and then click "Next."
3. Click "repair your computer."

Info: The boot selection failed because a required device is inaccessible.

I notice that when I run the newer OS installed, the previous OS's drive (Which is D: now instead of C:) has become unusable and when I double click it, it asks me to format the drive.

The data, that I had on my D Drive (Which is now C Drive for new OS), I had copied it to a network path and it is available. It was containing Windows 7 Users folder which I copied at that time when installing new windows.

I have copied that Users folder again to the new OS's C Drive thinking it would run again, but of no use.

Please please please...if someone can help...It is extremely required for me.

Thanks a lot in advance.