You should start by checking for malware on your computer. CCleaner and Malware Bytes are two great free products that you should use to scan / clean your computer. I recommend starting with CCLeaner to delete all of the temp files and other cruft on your computer. From there a full scan with Malware Bytes will usually clean most anything up. If you still have problems after those two it is generally a good idea to reload your operating system as there will most likely be a driver based infection on the computer which is hard to remove manually unless you know what you are doing.