I currently have have McAfee & Windows Secuity Essentials running on my laptop PC. Both have Firewalls, should I have both of these running? Is it slowing down my PC ? Also Windows Defender will not turn on, error 0x800705b4. Is this the reason? Thanks, PCstudent

It is recommended to only have one anti-virus solution installed at a time. Microsoft Security Essentials has come a long way since its inception and as it is free, I would keep that over McAfee. It also uses less resources than a lot of the commercial antivirus solutions out there. As for the Windows Defender issue, please follow these steps: Step 1 If you have any third party antivirus software and firewall disable them temporarily and make sure that the Windows Firewall is turned on. Then check if the issue reappears. Step 2 1. Open Run, and type in services.msc then press Enter. 2. In services window, locate Windows Defender service in the services list. 3. Verify that the Status is Started. If the Status column is blank, right click on the service and select Start. 4 If you get error trying to force start the Windows Defender service, try to change the Startup Type to Automatic, and then restart the computer. Hope the information helps. Please post back and let us know.If you found this post helpful, please "Vote as Helpful". If it answered your question, remember to "Mark as Answer". Rich Prescott | MCITP, MCTS, MCP [Blog] Engineering Efficiency | [Twitter] @Rich_Prescott | [Powershell GUI] Client System Administration tool

Thanks for your reply. I think I'll take your advice reguarding McAfee. As far as starting Windows Defender, after following your instructions, I recieved a message that Windows Defender started then stopped. Some services stop automatically if not in use by other services or programs. Thanks again, PCstudent

Hi again , I was just told that Microsoft Security Essentials has it's own version of Defender built in and will automatically turn off Vista's version. Is this true? Thanks, PCstudent

Yes, Microsoft Security Essentials (MSE) has it's own anti-malware engine and defender. So if MSE is working fine, you don't have to worry. Please revert back if you have any more questions. Hope it helps!Kunal D Mehta - a Windows Server Enthusiast | My first TechNet Wiki Article