DSL down as soon as I turn one networked PC???

Hi,Here I am again with hardware problems, although this one is quite odd.I have three PCs at home. All of them connected to a ADSL modem/router.1) Is a p4 2.2, connects through a wireless connection2) Is a p4 3.0 connects through a cable3) Is a FX55 connects through a cableThe DSL has been working fine for months already but today I started having problems with it.The DSL works with PC 1 and 2 on. As soon as I start the FX55 one, the connections dies. It is right at the moment I press the power button. even before the BIOS starts loading. If I turn the PC off, at any stage (loading BIOS or already within Windows), the DSL comes back on. It even happens if I disconnect the network cable.In this PC #3 I have the following:Gigabyte KNSC-939FX552 Gb RAM EVGA 6800 GTAudigy4NO MODEMNO ANY OTHER CARD.Has anyone has any idea what can be causing this.Thanks,Leo