I have this issue with many Intel based ThinkPads at my company. I contacted
MS and they have no solution for getting SP3 on these machines except to
reinstall from an SP3 slipstreamed CD, not an option for me. Here are the
instructions that I used to uninstall SP3 and bring my PC back to life if
Safe Mode doesn't work:
If you have a SATA drive then go into the BIOS and enable compatability mode
for the hard drive. XP does not recognise the SATA drive.
Boot from the XP install CD and go into the Recovery Console (when selecting
Windows installation choose option 1 NOT enter)
Go into C:\WINDOWS\$NtServicePackUninstall$\spuninst and type "batch
spunist.txt"
After uninstall completes boot normally and run WINVER
If it says SP3 still then browse to the
C:\WINDOWS\$NtServicePackUninstall$\spuninst folder and double-click on
spuninst.exe