1.
Reinstall. Windows XP is designed to be built on the machine it is to run on. It doesn't transfer well from one machine to another. I think you're saying you moved the existing operating system (hard drive) to a new motherboard and CPU.
You may need to perform a "repair" installation or a "new" installation of Windows XP.
I'm surprised you're able to boot to "Safe Mode". What was your old configuration. Maybe it's close enough to patch up. Maybe someone else has some thoughts on this...
You might be able to modify your "boot.ini" file to add additional invocation lines for the operating system to permit you to attempt booting with different versions of the "Hal.dll" and possibly "ntoskrnl.exe" (see the "/hal" and "/kernel" boot.ini option switches within
Custom Boot Menu in Windows XP).
2.
Blue Screen of Death (BSoD). Is there a BSoD when you attempt to boot normally? You may have to disable auto restart in order to see it.
Use the <
F8> function key during system startup to access the Windows Advanced Options menu. Tap the <F8> key once or twice per second as you startup the computer (or immediately after POST completes and
screen flashes black prior to displaying Windows XP logo with its processing bar display).
From the Windows Advanced Options menu, use the up/down arrow keys to select the "
Disable automatic restart on system failure" and hit Enter.
Hopefully the machine will stop on a BSoD. Record and
post back with the "exact" error message text and/or numbers plus any error string or software module (file name) it might name.
3.
Windows XP Install CD. Do you have the installation files available?