nordlead on 27 October 2010
1) take a known working device (like your PC)
2) plug it into the router with the cable that is currently being used by the PS3
2a) if this doesn't work then replace the cable
3) plug the network cable into each port of the router
3a) if any one of those ports doesn't work than mark that port as bad or just buy a new router
4) if everything works, than your PS3 is the problem
4a) try factory ressetting the system and be very careful to make sure all settings are correct (it should be pretty much automatic)
4b) try switching to wireless
if nothing works, your PS3's network card must be shot. The only thing I can think left to try is to plug your PS3 directly into the cable modem with a known working cable.
