Modem connection, or even LAN connection. If I connect without mains power, no problem. If I then plug in the mains power when connected, i either get the message LAN cable unplugged or the modem connection ceases to send/receive. Disconnecting the mains power restores either connection to normal! It's very frustrating - I've ran AVG antivirus, Pest Patrol, Adaware, Spybot and everything tells me there's no problem.