PS3 DNS error 80710102 (wired connection)?

I have tried everything possible to get online on my playstation3. I've used public and open dns, reversed the dns ip's, reset modem, disabled or enabled media server, changed the last number of ip address and/or subnet mask, used only primary dns or only secondary or even both, lowered the mtu speed, everything! I've started earlier today rebooting my ps3 to its factory settings and it'll be finished in about 4 hours, I don't kno that if after i do that, i will get online but everytime i try using the easy method, it always times out even though i get ip adress the internet connection fails, Same thing for manual, I always get ip adress succeded but i never get internet connection. Everytime I plug in the ethernet cable after rebooting the modem, the ps3 says no ethernet cable in or detected or something like that,but i still get the ip but no conection, I use a motorola sb5120 modem from comcast btw. I have read so many forums, visited comcast and playstation and I just can't figure it out, "Please Help"