When i try to run the System File Checker tool it gets half way through checking files then stops with the error message that it has performed an illegal operation and will be shut down. Does anyone know how to fix this problem??

It says a program has performed an illegal operation because the file checker opened a Windows file that if changed might damage the computer. One thing you could try is when you are changing the search settings, you could tell it to exclude windows files.

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Thanks for that, but how do i change the search settings in SFC?