Internet not working !!

Howdy. Im trying to sort out my dads PC for him at the moment. His internet has stopped working.

it used to drop the internet connection fairly regularly and show the "limited or no connectivity" symbol. A system restore would sort this out.

Now, that symbol is not present but no internet. It wont do a system restore either.Im suspecting an infection.

Ive found a few strange things happening as well:

The Windows firewall is set to "on" and is greyed out completely (wont let me turn it off).

I cant access the router settings (192.168.1.1) either.

Ive done a virus scan ( although definitions a week old) but nothing showed up. SO no matter what AV i run i cant update it first.

Im gonna try Malware Bytes without being updated and see if it throws anything at me before i do a Hijackthis scan.