As RealBeast said ,you 1st follow that guide.
Then check if problem is solved, if not then Go into browsers extensions , & check if Comet related extension is there , if its present uninstall it.
This should be enough.
Whatever you downloaded or you were installing if its not from proper , original , trusted website do not use it.
if you don't have a Antivirus/Internet Security software installed, for safety install one .
if you still think your computer is filled with virus/malware then install MalwareBytes you can use this software, its free for 30 days .