Hello JKB,
Go to Windows Update, do an Express scan, and apply all offered updªtes
http://update.microsoft.com
Once that is finished, can you verify the update installs? There are many
pre-requisite files which are needed from windows update and signature
update with windows defender will fail until you have these files.
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Go to the System Event log:
Start, Run, eventvwr.msc <enter>
Click on the System event log
Go to View, choose Filter, and choose "windefend" in the source control.
Look for yellow triangle entries that give the precise path and location of
what was detected, and use the button provided to paste the content of the
detection back to a message here.
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Could you supply some information on what your OS is, firewall, anti-virus,
other RTP programs, WD engine, etc?
Eиçel