If you see a message stating "it can't obtain IP address", then most likely something is not working on your end. If this is a PS3 and can't obtain an IP address, are you connecting by wireless or wired?
You state 2 different networks. All of your systems/computers/networks eventually make their way out through your internet connection (either being broadband/ISDN/4G). Start working your way backwards. Whatever the modem is, connect a reliable wired computer to it and verify internet connectivity. Move to the next hop and test again (wireless router or wired router). Keep going until you find an inconsistency. If then and only then everything is working, then it may be something between your console (ie PS3) and the network you are connecting to.
I too am having this issue. I don't think the standard, Check your cables, response is going to work here. Something is up with the PS3. I work in IT Networking and everything on my network is fine except for the PS3. So I really dont think it's the network. I'm revewing my routers firewall and port forwarding information and all seems to work when it does eventually sign into PSN. Since my PS3 is connected to a Receiver via HDMI with ethernet I'm going to disconnect it and try directly to the TV. The receiver and PS3 have their own wired connection. I'm also doing a port mirroring session to try and capture packets for more information. The only thing I've seen is some IGMPv2 messages to a public IP address. I don't think this is related. I have a static IP address so I'm not using DHCP. It just doesn't want to connect to the internet. I will also try to connect directly into my switch, a Cisco SG-200, directly and today I'm going to run a new CAT6 run. I'm currently using CAT5e. The CAT6 is 23 gauge which is a little thicker. This really shouldn't make much of a difference since it's a short run, approximately 50 feet. Also note that the connection to PSN is sporatic, I can get on sometimes. My internet is 50Mps down with 25Mps up. I have a Gig router with a Gig Switch. Yeah ... I'm a networking freak. I'll let you know how it goes.
I just went through something similar, though I had no problem getting an IP address...mine stopped when it tried to connect to the PSN (Failed). I knew the change I made that caused it (turned on my modem/router's firewall), it was just a matter of finding which ports I needed open in my firewall. I went to the firewall settings. I was able to set my firewall to maximum security so long as I opened 'PS2' ports (4658, 4659) and 'all remaining services/ports' (outgoing only). I had to do a custom setting for this (which extends the list of available ports), but I took notes on what was and wasn't open when set to 'high' protection then simply matched those settings plus opening the ones stated previously. I don't know if the PS2 ports were even necessary, but I left them open anyways. I don't know if that's any help.
LOWER YOUR ISP FIREWALL SETTINGS TO MEDIUM INSTEAD OF MAXIMUM AND IT SHOULD WORK
Edit: thread locked due to necro post