Will try it after the full scan has done, although I did "repair" earlier today to get the firewall running so should be ok from that perspective.
I use boot scan when I think something is adrift because in the past I have had good experiences with it finding things that didn't turn up or weren't fixed by normal scans. It's one of the reasons I use Avast. Some malware is quite adept at protecting itself / defeating AV / reinfecting on reboot and this has helped me before.
The PC concerned has an issue with web connectivity which may be malware related.