My advice and that of others on the forum would be not to install BTVirus Protect. It can cause problems on some computers and is a resource hog. Do a search of the forum to see the problems. There are far better free antivirus programs available such as Avast Free and AVG Free or depending on which version of Windows you have it could have Microsoft's antivirus already installed.
Which version of Windows are you using?
If you do want to install BTVirus Protect/McAfee make sure that you have uninstalled any other antivirus product that may be on your PC before you try to install it.