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#11
I'd boot into System Recovery Options to run a few passes of Startup Repair to see if it finds any issues. If you'll post back a screenshot of your maximized Disk Mgmt drive map with listings we can see if anything is obvious. Screen Shots
If this behavior started after any particular Update or Install, I'd use System Restore to get back before it.
Then start working through these troubleshooting steps to achieve and keep a clean boot, monitor the logs for repeat errors to resolve, use the System Resources which may yield clues.
I'd also install CoreTemp or Speedfan, google the CPU's maximum temp to monitor it.
Good move on AVG which only presents problems here and is recommended by no one.