Generally viruses can cause this type of behavior, regardless as I don't know which tools you've run, I recommend malwarebytes. Its infinitely more thorough than most scanners.
But I'm going to leave you a couple steps to try. Be sure to stop if one resolves the issue, no reason to continue if it does.
1) Malwarebytes: Install, run, let it FULL scan, click Show results, click Remove Selected
if it finds anything
Download link here:http://tinyurl.com/3d3ojaq
Download file. You'll have to trust me on this, if you HAVEN'T run this tool, it needs to be run regardless of what third party scanners you use. Right now its the best, XXXXX XXXXX been for awhile.
2) Clear your startup for conflicting programs. The only thing that should be running in your windows startup is your virus scan (which you can leave alone, or re-add later).
Start, in the searchbox type msconfig
and hit enter. Click Startup, Uncheck all boxes. If you get a warning, check the box, click ok. Restart.
3) Lastly, and it depends how long the issue, system restore.
Start, searchbox type system restore
hit enter. Choose a manual date (show more dates) and roll back to a date where you know it was stable.
Remember to return and click Accept should this resolve the issue, if not, REPLY
and we'll continue.