I did not read all of this, but let me toss this out and see if it helps any at all.
When you clone a drive, you cannot make both the drives bootable. It does not work that way. You must specify if you are cloning or mirroring the image to another drive to be used as a boot drive, or a backup. Very basically, the mirroring software will only put the boot sector of the drive on 1 disk or the other. Not both.
That would give you 2 individual fully functional independant working copies of the same software (Windows) which is illegal.
Now, if you have both disks in the machine, either one will boot as the motherboard will find the boot sector, (as long as both drives actually work and do not have physical problem) and the boot sector does not have to necessarily be on the same drive you are booting too! If you take the drive out of the system that has the boot sector on it, the other drive will not boot. You will get the no bootable device error.
Many people try to do this, make an exact mirror of their OS drive, take it out and set it aside thinking if their drive fails, they can just stick the mirrored one in an presto.....back to normal.
Don't know if this is your malady, or even close, but it does sound like this is what you have tried to do....it won't work quite like you may have thought it would
But you should be able to do a repair install.
Insert the XP disk, boot to it and start a new install.
When it asks if you want the recovery console or new install, choose new install.
Windows setup will start, and will find your drive with your current install of Windows on it.
It will ask you again if you want to do a new install, or repair the current XP installation.
Now choose repair.
It will run just as if it is doing a complete reinstall, but all your programs and files will remain intact and untouched.
This procdure will wipe out all your installed secondary hardware drivers, like your video card and motherboard drivers, so you will have to reinstall them as well. It will also wipe out your entire history of security updates from the Windows update site, so all of that will start downloading and have to reinstall.
But it will leave everything else just as it is.