One (and always the same) PC blocks Internet access on the entire network. It usually happens Sunday morning after not using it on Saturday, but it could happen any time.
What happens is that this computer uses up all network bandwidth and doesn't allow anyone else to access the Internet. The funny part is that this PC is still in sleep mode and no one uses it.
The way to cure this is to reboot the offending PC; all PCs on the network (including this one) then work normally.
We checked for infections on this PC but haven't found any yet.
Is there anything else I could do to troubleshoot this problem?