You will need your Windows Key (and disc!)
You do not lose any data (normally)
You may need to re-activate
You will need to do your Windows Updates again (presently SP3 from MS)
Remove all external power (basically the power cord, and battery on laptops)
Hold in the ON button, on your computer for 30secs
Plug the power cord back in
Turn on
Boot from your Xp CD (as above)
Using a different CPU in a computer can cause the system to scramble all data (it can happen) Therefore on any CPU c/o always do a repair
The only option is to run a checkdisk on the recovery (R prompt) screen
chkdsk c: /r
But you really need to repair (you must do this with the correct CD, otherwise you'll get this dual boot issue, that needs its own Windows key to work!)
It's probably DOA (Dead on Arrival) Yay I know something more than you (spelling anyway)
You stated that you replaced the CPU
This requires a Windows Repair to be done (usually)
Otherwise you can corrupt (basically files can be deleted or destroyed on your HardDrive) possibly. (I need to cover all angles here )
You know people from outside US don't know what white city means (well I don't)
Don't bother replying I'll google it one day (seems a few go there from time to time, I imagine this city all white lol )