You'll need to leave your AV (use free lightweight Microsoft Security Essentials
or Avast for best performance) checked in msconfig>Startup. Check also in >Services tab after hiding all MS Services that everything except AV is unchecked.
Check optional Windows Updates for newer drivers. Look in Device manager for any drivers in error, and update your drivers.
Follow Lemur's suggestion to disinfect your System thoroughly.
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If these fail check the logs and System Resources for clues working through these troubleshooting steps