Windows updates not installing

[pursuant]

I've got windows Xp and service pack 2 installed. Up till a few weeks ago I was getting the auto updates from windows. Then I had some problems with java updates. I was told that windows installer needed to be reinstalled, which I did, no luck with java updates, but then I was getting windows updates when I shut down, saying they would be installed before windows closes. This has happened 3 times so far and the updates have not been installed . I tried a manual install and I was told to update the window installer which I did. I thought I had downloaded several security patches but after each was downloaded they failed to install. Then I tried service pack 3 and it seemed to download  but afterwords it said it too had failed to install. I am stumped.
Any advice appreciated

Thanks

[Dusty]

The quoted response courtesy of 8Bamboos.

Re-register the Windows Update DLL with the commands below

Click Start, click Run, type cmd, and then click OK.

Type the following commands. Press ENTER after each command.

regsvr32 wuapi.dll
regsvr32 wuaueng.dll
regsvr32 wuaueng1.dll
regsvr32 wucltui.dll
regsvr32 wups.dll
regsvr32 wups2.dll
regsvr32 wuweb.dll

Attempt to run Windows Update

It worked for others with the same problem.

Good luck

[pursuant]

Thanks....did it and it seemed to have worked as I downloaded service pack 3, and it installed and started to update when it was copying new files I got a message saying Windows service pack KB 936929 window update of system files cannot copy atapi.sys.It asked if I wanted to go ahead with the install, I did. About half way into the setup I got a "service Pack 3 setup error access is denied" Not sure what that is? So it uninstalled everything and at the end I got a message saying the service pack install was not completed and windows xp may not work properly. So I did a reboot and it seems windows is still working properly ( Thank god)...very perplexing.
Edit/Delete Message

[Dusty]

Yes, SP.3 still generates errors on some systems, don't know why, but after I installed all updates since SP.2 it (SP.3) installed without problems.

Good to know that re-registering the update dll's solved your original problem.

Good luck

[merlin]

Get a decent firewall...not win.oooo

[pursuant]

Actually I still don't have service pack 3 installed and after the message saying that XP may not work properly I don't know if its worth it.
 Are you saying that the Windows firewall caused the problem ? The Access denied message I got when I tried the install?

[Dusty]

Whilst agreeing with Merlin that you should have a better firewall than the one supplied with XP I don't understand what he is inferring in his post.   You may already have a third party firewall running, it's not been mentioned in any of the foregoing posts, and I doubt if the XP firewall has any bearing on your problem with SP.3. 

Have you installed all the post SP.2 updates

Suggestion: Download SP.3 manually to your hdd then you won't have to re-download to re-install it.

[pursuant]

I assume I have all of SP 2 updates. I have to keep remembering that I need to use IE to check this information, I use Firefox so Its hard for me to keep track.
I have
Security Update for Windows XP (KB946648)
I don't have
Windows XP Service Pack 3 (KB936929) and I did get this error code
Error Code: 0x80072F78

Thanks