You might have malware on your computer. Download Malwarebytes Antimalware. Update it and run a full scan. If it doesn't find anything, run it again in safe mode. The easiest way to get to safe mode that I've found is turn your computer off with the on/off button, don't shut it down the normal way.
When you restart it you should get a screen saying something about the computer not shutting down correctly and it gives a list of options. Use your arrow keys to move the cursor to safe mode and hit enter. It will scroll a whole heap of stuff on the screen then start windoze. All your desktop icons will be huge. When the scan is complete, restart your computer the normal way.
Make sure you have an active virus scanner that updates at least daily. Try and avoid Norton or McAfee. They are both good programs, but as they are so polular, the virus creators create their malware to get around those. A good free one is Avast.
