update windows and defender

Apx 2 months ago we bought 2 new computers, both hewlett packard with vista home premium installed,, practically since day one we have not been able to update windows from the site or windows defender ..I made sure I did not have any firewall up .. I had also installed comodo antivirus which I might add I can not update either ... I actually uninstalled it last night thinking it might cause the problem, but could not reinstall . I downloaded spybot and when I try to install I get the error that I must be connected to the internet .. malwarebytes gives me the same error....I can download and install anything else ..games music etc with no problem just anything that will protect or heal my pc like windows defender etc I cant ..... this is happening on both computers.. I dont know if this is a software or virus . please someone help . I would like to update windows, defender and my antivirus programs :-cry

 

Hi, just my 2pence, could there have been an antivirus on the computers when they were bought as there usually is, which you can use for a short time. Boneyeye

 

well I rebooted in safemode . still was unable to download any updates for windows . defender or malewarebytes. I did however run a scan with the version of malwarebytes I have already and it found 5 trojanDNS changer.. in registry but I removed them .. tried to go back to download updates and still no good ....... :-(