Swap hard drive to another computer - fail

Hi.  I am running a Dell 6500 with Safeguard 5.50 enterprise.  I tried to move the hard drive to another 6500, however, it goes into the, "Boot loop" problem (looks like it's going into Windows but loops back to POA screen).  I've changed the bios hard drive setup to ata, then back to ahci.  I've tried the f6 and f9 keys.  I attempted to restore the master boot record.  It says something like, does not match the machine.  Any ideas?  No rush since I put the hard drive back in the original - the user can get by for a while.

Thanks.

JB