Does the issue persist while you are watching some videos stored on the hard drive, while you are playing games or using some kind of software? Have you tried with another internet browser? I strongly recommend you to install the latest Windows updates. Is reinstalling the OS an option? If it is, I would advise you to do so. This way you may fix some errors and software issues. If reinstalling is not an option, update your antivirus and do a complete system scan.
Hope this helps