As for the DNS issues accessing sites, often this is cause by the hosts of those sites changing DNS configs causing wrong info to be propogated through the internets DNS servers. Sometimes a genuine PlusNet DNS server issue occurs, in wich case the backup servers should take over the load. Also sometimes updates take a while to propogate through all the PlusNet DNS servers so when a new domain is created or an IP address (host) changes, some may have the new IP addresses for a domain and some may have old ones which have not updated automatically yet. DNS server changes can also take 48 hours to propogate to all internet DNS servers.
Sometimes WIndows will cache bad or wrong DNS entries causing websites to be not found.