So if both drives attached you see a boot menu with 2 boot options?
If you detach one of them it boot fine (from the other one).
Attach the old none working disk only. Or attach both.
Boot from Windows 7 system repair disk or Windows 7 install dvd. Then do Partition - Mark as Inactive
Mark all volumes inactive on NON BOOTING disk only! To find correct volumes.... check the size of volume. Does it boot now?
Both are sata drives? Can you swap the sata cables, so working one is tried first