Windows Defender switching off.

I installed Windows defender about a week ago to my Windows XP Home. On setup I elected to display the icon in the icon tray and checked the box, 'Always' displayed. The only other box not ticked is * (Changes made to your computer by software that is permitted to run). On boot up the icon for Defender displays with a tick and is in the on position.
I also have AVG 9 with ID protection and Avast.
As the icons load and the AVG and Avast icons appear,the AVG ID is active and scanning. The Avast icon has the yellow exclamation embedded in it until it becomes active and it is at this point that the exclamation transfers to the Windows Defender icon and switches Defender off. I then have to click the icon and switch Defender on.
I have read other posts in another place,however,I can't find anything to rectify this problem. Could AVAST be the problem ?
Joker

 

Thanks TonyT. I have uninstalled Avast as you suggested,however, Windows Defender is still switching off.
Joker

 

Hi there again. The only time Defender switches off is on initial startup when the icons are loading into the bottom icon tray. Once I click on the Defender icon to open the window and turn it back on,it stays on. I go through this process every time I turn the computer on. I use CCleaner on a regular basis after any lengthy browsing period. Any bearing? The only other program I have installed is Spamfighter Pro.
If I do a full scan with AVG during the course of a session on the computer,it doesn't effect Defender by turning it off.
Joker

 

Back again.
If you go into the Defender interface window and click tools,then options on how you wish defender to run, there is a question as follows and the box beside that question is unticked......Choose if Windows Defender should notify you about.
*Changes made to your computer by software that is permitted to run.
I am not sure what that means or if that box should be ticked ?
Joker

 

I have been using both Windows Defender and an anti-virus (currently Avast! Home 4.8) for years. I do not see WD as a traditional AV product. It is more of a "behavioral analyst" similar to ThreatFire which I use also.

I sure would not trust WD for traditional anti-virus work.

 

Scout, Windows Defender is not an anti virus product and Joker is not using it as such

 

I guess I misread his post.

 

Thanks to all who replied to my post. I have decided that it is not too much of an effort to turn WD back on each time I boot up. With my limited knowledge,I feel that by having AVG9 with ID protection,Spamfighter Pro and Windows Defender I am covered in the main areas. I find AVG a good program. I am vigilant when browsing the net and am not inclined to go near sites that are known to be suspect. Regular scanning is practised.
Finally I must compliment Windows BBS on their forum site. Thanks again....see you all later.
Joker