Make sure you are connected to the correct DNS and DHCP servers.
Go onto another computer in the house (if you have one) and go into command prompt (you can press windows sign + R) type in 'cmd'. When command prompts open, type in 'ipconfig /all'. If you are using wireless, look under wireless settings else look under the correct settings. Compare the DNS and DHCP server with your computer and see if they match.
If you do not have another computer, do the same above on your computer and let me know your DNS server. If you are getting internet, you probably have the correct DHCP server, but your router has been hijacked to send you to an incorrect DNS server (the one that does the google downloading).
The reason why I suspect it is a DNS hi-jack because you are not finding malware on your computer that would be causing this. Unless it's a new maleware, it should definitely be detected (it may be a new maleware). However, using a different browser should fix this problem as maleware is not usually written to work in multiple browsers (because they have different structures).