Bullfights, the best you can do is to re-attach the HD to the old computer, and do a system restore using a backup image, if the HD still refuses to boot. If you have no backups then use install DVD to do a repair install as told in this tutorial: Repair Install
In worst case scenario do a reinstall NOT FORMATTING THE HD, which creates a Windows.old folder which includes your user folders and data.
I am very sorry I am not able to help you. On those very rare occasions known to me when this method has not worked, I've seen no pattern as of why.