That's a problem.
You don't say WHAT error occurs if you try to access the recovery partition, so we can't help with that at the moment. We can't even form an opinion on the question if it's related to changing the mobo or not.
But even if it was accessable and the recovery should start, there's a fair change that it says that it's not the same Compaq it was and refuses to install.
Such a thing happens with OEM licenses. They are only valid on the original machine and not transferable to other machines, neither technically nor license-wise. If that's the case, all you can do:
- contact HP/Compaq customer support and see if they can offer you a solution
- buy a new XP disc and license.
These problems shouldn't have occurred if the mobo and processor were replaced by exactly (that's exactly enough) the same new ones. A random new other motherboard gives these troubles indeed.
I have a Compaq desktop with Windows XP, which, not so long ago, the motherboard and processor get damaged and where replaced. Yesterday I wanted to restore the desktop to its original state, but I forgot than the motherboard and the processor where replaced. Now when I startup the desktop, an error occurred and XP doesn't start not even I Safe Mode. What can I do? By the way, my desktop didn't come with Windows XP CDs, instead, it has a partition, but for some reason I can access it now.