Download and use malwarebytes, in addition to your virus scan Malwarebytes.org
Next time you have the problem go to event viewer and look for errors
Check drivers from device manager
Make sure your video card is working and current.
Type memory diagnostics in search and take that test.
Try running in safe mode.
Switch Browsers, you may like try thunderbird.
Go to tools>internet options>advanced>reset. You will have to reinstall all browser add-ons after this procedure.
Begin by making a system restore point, so you do not have to reuren with bigger problems than you have now.