Can't install Service Pack 3 on XP

I managed to install SP3 a while ago but the HP Presario desktop computer was running so badly that no amount of clean ups did much good so I did a complete factory reset direct from the recovery partition.
Now it's running great and I can see it has SP2 included in the reset but all attempts at installing SP3 have failed
My first attempt was to try and get SP3 by running Windows update
This didn't work because I discovered that now Win Updates only works with SP3 creating a catch 22
I searched through windows help and found out how to manually download an install SP3
I downloaded it and ran the installation and guess what? It failed and I got an error code which I'm afraid I didn't note down
Each attemot resulted in the same error so having noticed during the installation process a restore point was created I ran system restore so that I could start over
Now it starts the process, creates a restore point and tells me its completed but it obviously hasn't because it's showing to still be on SP2 so it looks like I'm stuck
Computer is working fine but cant update windows.
Normally I'd live with it but on hearing that Windows will stop supporting XP next April I feel it's important to get the system up to date while I still can
If anyone can give some easy to understand advice while I have some hair left I'd be very grateful

Compaq Presario SR2019UK
It has an AMD 64 3500+ processor
Windows XP Media Center Edition version 2002
Attempts to use Windows Update result in Error Number 0x80190194

Simple to understand advice please as Microsoft help pages are either missing the point or far too daunting

 

Het Juliasdream, try installing sp3 from here, but use the Download@Majorgeeks, NOT from the Authors site, http://www.majorgeeks.com/files/details/microsoft_windows_xp_service_pack_3.html

 

juliasdream...hello, were you by chance attempting to install SP3 from a backup hard drive. I noticed recently that it wouldn't install from a remote drive location on my PC. The installer apparently has to be on the main drive.

The updates is the standard one for an XP system that doesn't have SP3 installed...

 

Apologies...I mean updates error