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These are being ran one at a time with all others disabled yes the machine completely shuts down without warning. Scanners do not count as Antivirus programs.
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Multiple AV's can butt heads with each other, let things in, and slow down a machine CONSIDERABLY. norton 360 internet security & AVG Free Edition) you must uninstall all but the one antivirus program you trust. Remember, if you have more than one antivirus program INSTALLED (I.E. Can you give us a little bit more information? When you say shut down with the machine do you mean the machine powers off suddenly without warning? Also, try Malwarebytes, combofix, eset online scanner, or clamwinportable.
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