boot problem

I have cloned a Samsung 80gb drive to a Western Digital 160gb. This has been succssful, both drives appear in Disk Management but not in My Computer on XP but both show on Win 7. With both drives connected I can boot into either OS but when I remove the Samsung Drive I can only boot into Win 7. I get a message directing use of XP installation disk to "Repair Computer". I only have an XP pro disk not the Home Edition with which the computer is loaded. The XP Pro does not give me the option to "repair your computer". The error page seems to indicate a missing "ntldr"
Help Please !

Regards,

Wychwar