Having an anti-virus running 24/7 could be the cause of your problems.
Next time you experience the issue, check to see if the anti-virus program is running a scan.
Other than that, follow the steps located here:
!---IMPORTANT: Please Follow These Steps Before Posting---!
Keep us posted on how it goes.
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"Come forth for the cattle call
Confront the evil river you can't control
Wicked ways and venomous eyes
Just human nature in disguise..."- Clouds over California