Thanks for the suggestions Shane but, as I said in my last post you can not reinstall Windows Defender only because, being integrated in Win Vista, the operating system does not allow it.
I also tried the suggestion to run “System File Checking tool (sfc.exe)” and when it has completed 78% of the test is stopped and gave the following message: “Windows Resource Protection: Can not perform the requested operation” .
At this point I do not know what to do, do you have any other suggestions for me?
Thank you. Felix.