Boot order issue.......

When I originally installed 7 on my dad's PC, I disconnected the other 2 hard drives (I did not want the boot selection screen popping up all the time). Everything has been working fine (he uses XP, so I use the BIOS to select the hard drive boot order when I want to boot into 7). Yesterday I disconnected the Windows 7 hard drive, so that I could clone his XP installation over to the secondary hard drive in the machine (the primary & secondary drives are 80 GB SATA units, while the Windows 7 drive is a 30 GB IDE unit). When I was finished, I shut down the machine & hooked the Windows 7 hard drive back up. For some odd reason, the machine boots into 7 no matter which drive is selected first in the BIOS boot order. I cannot figure this one out. With the Windows 7 drive disconnected, the machine boots into XP just fine. Does anyone have any idea what could be causing this to happen?? I cloned the XP drive once before & did not have this problem(I do it every couple of months so that he has a complete image should the main hard drive fail). Any input will be greatly appreciated. Thanks in advance.

I decided to disconnect the secondary SATA drive (the one I cloned the OS to) & run it through a boot cycle with the primary SATA drive & the IDE drive hooked up (the one with 7 on it). It booted to XP just fine. So after I did a small update that Windows needed, I shut down, hooked up the secondary SATA drive again & it is booting like it should now.