SP 4?

I have a Win 2k server, also running Exch 5.5 on an NT4 domain. When starts, automatic updates service fails. Have had some RPC errors as well. Have tried several things, but most troublesome development is that I can’t install SP 4. It seems to hang & the CPU runs at 100%. It was SP2, I have tried SP 3 & went fine, but no improvement. Any ideas out there?