anti-virus problem

[#1]

I have XP with AVG Free 2011, Spybot, Ad-Aware and Zone Alarm. Yesterday I updated AVG, but then found it wouldn't scan anything but the Rookits. I am taking to AVG Forum about this.
In the meantime, I wanted anti-virus cover so I installed Avast (without uninstalling AVG). I ran a scan, but nothing was found. Today I try to use my pc, but couldn't get past the desktop (everything I select just causes the egg-timer to appear but nothing happens - I gave it 5 hours to do something once, but there have been many other attempts to boot up). At this point whatever I selected the pc froze. I then rebooted and selected Avast by clicking on its symbol at the bottom of the screen. I went in and stopped the shield. From then I could get into Control Panel and tried to uninstall Avast. The uninstall started, but after Avast asked me to confirm I wanted to uninstall, the pc froze again. Now when I boot up, I am back to not getting past the desktop.
Any suggestions?
I would rather not have to reload XP because of the knock-on to reloading all the other applications. However, I dont know how to use Repair on my XP CD. I can get to where Repair shows C:\Windows, but there is no guidance as to how proceed with any repair.
Please help. Many thanks. Sorry for the long tale of woe.

[#2]

First thing is to remove both anti virus programmes using these removal tools - you shouldn't have two running at the same time
http://www.avg.com/us-en/download-tools
http://www.avast.com/uninstall-utility
If that doesn't fix the problem try rolling back to an earlier checkpoint using System Recovery

[#3]

Thanks OldJim, but I cannot get past theDesktop without the pc freezing. However, your suggestion did nudge my old grey cells, and I tried rebooting in Safe Mode. This gave me the choice of working in Safe Mode or using System Restore. I tried a few System Restores going back to about mid-January, but they wouldn't work (the pc froze), so I tried Safe Mode. Now I was able to get to Control Panel and uninstall AVG 2011, and then also Avast. After this, I needed to go to AVGs web-site and download an uninstall program, but now I can use my pc.
I have yet to reinstall Avast, but I may look at the AVG Forum to see if they have a solution to my original problem, before I use Avast.
Many thanks from grumpyxch - that's Grumpy in Christchurch, so not too far from Old Harry Rocks

[#4]

Word of advice, Ditch AVG.

[#5]

AVG is pretty bad but the latest version of Avoid oops I mean Avast has my desktop taking 5 minutes to actually get from the login screen to a functional desktop. The hard drive LED stops lighting up and it just seems to sit waiting for something.

[#6]

I normally recommend Avira as a free one

[#7]

It seems my original problem (with AVG 2011) was, it didn't like my version of Zone Alarm. Have installed latest ZA, and AVG now scans.
Hooray!!!
Thanks for your help OldJim

[#8]

ZoneAlarm again? 
Penneck, your security software is the perfect combination for 2003 but it's 2011 now and things change.  For example, the AVG of 2011 is radically different to the AVG of 2003 and runs badly on most XP computers I see.  Personally, I prefer Microsoft Security Essentials - but I don't have any experience of Avira that Oldjim recommends.   

[#9]

Avast runs well on XP and with Zonealarm