You're off topic for this forum, which is dedicated to
Windows Live OneCare.
You need to post here.
Windows 7:
http://social.answers.microsoft.com/Forums/en-US/category/windows7
However, since you mention Symantec *and* Microsoft Security Essentials, I can tell you that you need to remove all other security software before installing MSE. Uninstalling isn't enough with Symantec,
McAfee, and other similar products.
You may need to use a cleanup tool to remove your prior security software:
http://social.answers.microsoft.com/Forums/en-US/msestart/thread/407bf6da-c05d-4546-8788-0aa4c25a1f91
Be sure to review this post:
Check list for installing Microsoft Security Essentials
If that fails to resolve the problem, open an email support case:
To open an email support case, start here:
https://support.microsoftsecurityessentials.com/
-steve
~ Microsoft MVP Windows Live ~ Windows Live OneCare| Live Mesh|MS Security Essentials Forums Moderator ~