What are you missisng?... Well, it depends on up to what point you got when attempting to Repair the installed Windows XP. What I gather from your comments, is that the Hard Drive may be working normally in the new motherboard, but the Repair of Windows XP is either interrumpted or cannot continue?... If so, it may be the version of Windows XP installation disk does not allow Repair installations... That is why I ask up to what point did you get... click on the links for a Windows XP installation tutorial, and tell us up to which of the installation screens you got... that would give us a better idea of what the cause may be.
OK, since you did manage to repair-installed XP, and the Hard Drive seems to be in good condition... the problem seems to be related to drivers... maybe a driver the motherboard needs that wasn't included in the Windows XP installation... the question now is which driver since you need to access XP to tell... but I'd bet you can boot that XP with a simple boot.ini edition, the only complication would be if you have already attempted to logon in Safe Mode and haven't been able to and since you didn't mention it, my guess is you didn't try.
First off, in your new XP installation, go to Control Panel \ System \ Advanced \ Start and Recovery \ Settings \ and uncheck "Automatic Restart" (this will help you read the blue screen in case it comes up again, and so you can make a note of the error numbers shown on the blue screen).. next click on the Edit button (this opens the Boot.ini file), and next go to the start menu, and save a copy (save as) in a secure place in your Documents folder. Next on the active Boot.ini file select the last line, copy it and paste it right under the last one... the edited Boot.ini file should read exactly as follows:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect
multi(0)disk(0)rdisk(1)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect
Save the changes made to the file and close it, and next restart the computer... the OS selection screen should come up during the reboot... select the second OS option and your older Windows XP should boot right up... and if it doesn't, reboot the computer, again select the second OS boot option but this time press F8 immediately after pressing Enter. The Safe Mode options list should appear on the screen, where you should select Safe Mode with Networking so you can download and install the necessary drivers.
To visually check which drivers are necessary, right click on the My Computer icon and click on Manage, next Device Manager and see which device has a yellow exclamation or question mark. Right click on that device and select Update driver, next Select "yes, only this time" and press Next. If the driver is not successfully installed, repeat from update driver and this time select "No, not at the moment", click Next and Select "automatically install this solftware (recommended)" and click Next.
If still you can't install the necessary drivers... Logon to the newly installled XP and following these same steps, see under the same device, what the difference is from the working XP to the other (different device name, a different driver installed, etc). You can see the installed driver files in: Device name\right click-Properties\Driver\Driver details. With this information on hand, you can search the web for the appropriate drivers.
You may be wondering how come the new installation does work with the drivers included in the Windows XP installation CD(?)... Well, my only explanation would be that the XPCD installation program didn't detect the difference or it may not be set-up to replace every installed driver or it even may be that the necessary driver isn't signed so it didn't install it. Some time it happens that the Device Manager doesn't update drivers that are best for a given device just because they are not signed or because it sometimes does't replace apparently working drivers.. it often says that it "can't find a more appropriate driver than the one installed", so maybe that's what happened during the installation. This would be expected if you consider that a Repair installation is not always concluded perfectly. If I'm right, you should be able to confirm it. I have done a good number of XP installations, and sometimes some device drivers are not updated from the CD during a Repair installation.
In case Safe Mode doesn't work, make a note of the blue screen error numbers and post them here.
The bsod error i got was 7B. THe 2nd hex code was 34 which suggests a corrupt hd driver. I tried a Repair of the OS yet again, but it didn't help. I ended up doing a fresh install over the existing Windows directory and now I can boot to that drive.
I wish I could go back now though because I've lost the ability to run any programs and all my settings and any data in the My Documents directory is now cleaned out.
You should have asked for more detailed information before proceeding with a fresh install... you still had several options like:
a) Load fresh SATA drivers during a Repair Installation, or
b) created a new partition in the same Hard Drive and installed Windows XP on it.
From a new installation you could have tried different approaches to solve the problem,
1) you could have moved your programs to the new installation,
2) You could have rescued licence keys to fresh install the programs... I know of an application that can remotely rescue licence keys.
3) You could have rescued-backed-up documents which btw I thought you had already backed up since you mentioned you could apparently do anything with the drive.
As for the fresh install option you should have asked or read about it... it's not like a repair-reinstallation in which you keep documents and running programs. Rather than doing that type of installation in the same drive, you should have installed a new copy of Windows XP on a new partition... and eventually you may have found a way to solve the BSOD.