Might try IBM's support documents
http://www-307.ibm.com/pc/support/site.wss/document.do?lndocid=MIGR-50574
Frequently Asked Questions about Microsoft Product Activation
http://support.microsoft.com/default.aspx?scid=kb;en-us;302878&Product=winxp

I think you have a UAP (Unknown Acronym Problem.) I looked up MPA and found
nothing useful, so whatever you mean, maybe you need to spell it out.

Also, a definition of "won't boot" might be useful. If you mean no power, no
lights/fans, odd beeping, doesn't get past the bios screen, then you've got
a hardware problem. Could be something as simple as a connection or card
that got nudged when you were swapping drives. Or, it could be that
something actually got damaged in the process.

If you mean that you further in the process so that it's actually starting
to load windows, but you don't get fully into windows, then it's a software
issue of some sort. If you give a description of when it fails, what error
message, etc., somebody can help you. It could be as simple as a corrupted
file, or it still might be a hardware issue -- cable not seated fully,
memory got zapped, etc.

As far as reactivating hardware, I have no idea what you meant to ask, but
if a piece of hardware has actually been damaged or destroyed, there's no
way to bring it back to life. You simply replace the part.

Maybe you're thinking it's a bad driver, but that's pretty unlikely.