You have BitDefender installed ?
You can't have two antivirus applications on your computer ! Certainly not real-time, and even having one AV aplication for on demand scans, not real-time, can cause problems.
The correct procedure for removing and reinstalling McAfee involves using the MCPR tool, see elsewhere on this forum for instructions.
This is, I hope, XP SP3? Enable Windows Firewall for protection during the following procedures. When McAfee is finally installed it will automatically disable it.
Uninstall Bitdefender in the normal manner from Control Panel/Add or Remove Programs. Then use the removal tool:
Then do the following:
Download the http://www.bitdefender.com/uninstall
First right-click on the red BitDefender icon near the system tray choose on Exit.
Wait a few seconds. Afterwards double-click on the BitDefender uninstall tool.
You will need to reboot your computer for the changes to take effect.
1. Uninstall all McAfee programs through "Add or Remove Programs" in Windows "Control Panel".
2. Use the MCPR tool, see this article: How to remove supported McAfee consumer products using the McAfee Consumer Products Removal tool (MCPR.exe). This will remove all McAfee remnants from your computer. (you must have Windows Vista, XP or 2000 SP4 to use this tool)
3. Launch Windows Explorer and delete all McAfee files in "Program Files" but especially in "C:\Document and Settings\<user>\Application Data" and "C:\Document and Settings\All Users\Application Data". You have to set Windows Explorer to show all hidden files and folders (Tools > Folder Options > View tab). Just delete the McAfee folders even if they are empty in all the "Application Data" folders. Can be more than one!
In Vista: C:\Program Files, C:\ProgramData and C:\Users\yourname\AppData\Roaming
If you can't find these files don't worry. It just means that MCPR has done its job.
4. Reboot and redownload/reinstall your McAfee products directly from your account at the McAfee web site NOT from any CD that you may have.
If you are McAfee direct customer, go to https://home.mcafee.com/Secure/Protected/Login.aspx and log in to download your McAfee products.
If you received your McAfee products from your service provider, please use the list below to download your software.
Comcast users should go to http://security.comcast.net/ and log in to download your software.
DELL users should go to https://us.mcafee.com/root/login.asp?affid=105 and log in to download your software.
Gateway users should go to https://us.mcafee.com/root/login.asp?affid=370 and log in to download your software.
eMachines users should go to https://us.mcafee.com/root/login.asp?affid=365 and log in to download your software.
MSN users should go to http://membercenter.msn.com/ and log in to download your software.
AOL users should go to http://daol.aol.com/safetycenter and log in to download your software.