Problem replaceing Seagate HD

I am attempting to replace a Seagate Barracuda ATA iii HD in a Compaq Deskpro EN slimline. It will take an identical Seagate HD with no problem. However, when I try 5 other HD's the computer recognizes them, tells me what kind of HD it is saves the HD configuration when I press the F! function key.

However, in every case I receive the following message
NTLDR missing
Press any key to start.

I have seen this message when a non-system floppy disk is in the A drive but there is none.

As soon as I put the Seagate HD in the system works .

Any suggestions?

 

You will have to format and install windows.

 

How are you copying the old drive to the new one?

 

I ma not copying from the original. These replacement computers already have on O/S on them and some data. I took them out of other computers that were all right.

I could probably reformat them but were wondering why I just can't substitute them for the Seagate.