BleepingComputer.com: Windows Defender keeps being stopped

I have a desktop PC with Windows Vista Ulimate and avast! 4.8 professional anti spyware package. Until recently Windows Defender would launch OK each time I started the PC. However, when I now start the PC a Windows Defender alert icon appears in the bottom rhs of the screen. When I click on this icon a warning appears to say that Windows Defender has been turned off and the PC is not protected from spyware, I can start Windows Defender manually by clicking on the Start Now option that apears in this warning.
I have set Windows Defender to start automatically in Services and clicked on Run as Administrator but neither actions has resolved the problem.
If anyone can assist I would be very grateful.
I have had the PC since Noember 2009 and have not had any problems until this recent issue of Windows Defender failing to start atomatically. Could it be malware related or a program setting ?
Any advice would be appreciated
NONIC

Windows Defender gets disabled when other security programs are installed:

Worth while information

Hi Bleepin Madman
Thankyou for your response and also the link provided. I wasn't aware of a conflict between Windows Defender[WD] and the avast! antivirus package as WD has been starting up automatically until recently.[WD=antispam / avast=antivirus].

If I leave WD turned off will I still have anti-spam protection with avast anti-virus?

Steps 2 & 3 of the Microsoft fix in the the link provided recommend removing WD then re-installing. ie

2 If this issue is not resolved after you complete step 1, uninstall Windows Defender, and then reinstall Windows Defender. To do this, follow these steps:

<LI type=a>Click Start, click Run, type appwiz.cpl, and then click OK. <LI type=a>Click Windows Defender, and then click Remove. <LI type=a>Follow the prompts to uninstall Windows Defender.

• To reinstall Windows Defender, visit the following Microsoft Web site: http://www.microsoft.com/athome/security/spyware/software (http://www.microsoft.com/athome/security/spyware/software)

3 If this issue is not resolved after you complete step 2, uninstall Windows Defender, use the Windows Installer CleanUp utility, and then reinstall Windows Defender. To do this, follow these steps:

<LI type=a>Click Start, click Run, type appwiz.cpl, and then click OK. <LI type=a>Click Windows Defender, and then click Remove. <LI type=a>Follow the prompts to uninstall Windows Defender. <LI type=a>To use the Windows Installer CleanUp utility, click the following article number to view the article in the Microsoft Knowledge Base: 290301 (http://support.microsoft.com/kb/290301/ ) Use the Windows Installer CleanUp Utility to remove Office 2000, Office XP, or Office 2003

• To reinstall Windows Defender, visit the following Microsoft Web site: http://www.microsoft.com/athome/security/spyware/software (http://www.microsoft.com/athome/security/spyware/software)

I could not remove WD as it is not listed as a program in Vista.
Do you have any advice please.
Thank you
NONIC

Just leave the Windows Defender service disabled, and you will be set.

Have disabled Windows Defender in Services. All appears to be OK. Thank you for your advice.
NONIC

Glad the issue is resolved, come back if you need any other help.