What anti-virus software you use? You said you download one but it cannot be installed because hp computer, but maybe it is because of your Windows version.
and does the virus alert always appear on your PC? If so, you may get adware which ejects fake pup-ups. You need helps from the following link:
What content are the ads about? I mean, your computer may get adware, dubious registry keys changes or virus inside. I take Static.brit-method.com as an example (just want to make matters easier, if your computer is not infected with virus like this, you still can learn some knowledge about virus)
