Windows tries to start up then A screen flashes real fast (can't tell what it says) then it tries to start up again and I get the screen with options of Start windows normally, last known good configuration, safe MODE ect. It will start up in safe made. Last known good configuration will not start-up.
I can start it in safe mode and use system restore to restore it to XP SP2 and it runs fine.
But I want SP3. What can I do?
Seen this link from MS support? Check also this one for other possible information.If it were me, and I really wanted SP3, I would boot to SP2, backup my files, and do a clean install.  That should take care of it.  Of course, I also like the feel of a freshly installed OS and knowing all my old junk over the YEARS is no longer hiding out and scattered all over my PC. Quote

I also like the feel of a freshly installed OS and knowing all my old junk over the years is no longer hiding out and scattered all over my PC.

Microsoft Windows XP SP3 Upgrade Utility PREVENTS continuous system restarts or "Stop: 0x0000007E" errors after upgrading to Windows XP SP3 on systems with AMD processors.