XP locks up on restart after installing SP3

[NB STAN]

I have a 2nd older computer, 1/2 decent, and after installing sp3 it locks up
on a reboot, I have formated the drive and reinstalled XP home and a few
times now. I have had it work using an older sp3 rc1 I have on a cd. Why
does it do this? I do not want to waste another day having to reinstall
windows again. I forget about the sp3 issue and installed it and the comp
is locked up totally again.
Any ideas of what to try?

 

[KG]

Just stay with SP2, it has all you need