using a wrt54g. yes its comcast. hooked up to the router.
Okay we have a router in the mix here which creates a whole new reason why you could be having issues to which comcast has no control over at their end.
Give me a few moments, I just want to check the lay out of your routers firmware and its settings.
I need to ask you have you ever entered your routers setup utility and enabled use router as DHCP server?
This is very important, it allows your router to assign your devices an IP address from a list it creates starting with the next one up from its own IP address.
For example routers IP would be 192.168.1.1 now it starts assigning devices an IP starting with 192.168.1.2 then 192.168.1.3 the last digit changes up 1 for each device requiring an IP address.
Also sense Comcast is not a DSL service, you have to set the router to allow get an IP and Mac address automatically from Comcast.
DSL connections usually require a name and password, which is assigned by the ISP, this is not needed for Cable modem connections.
By the way, if your router is not allowing you into the WAN, then your status lights on your Ethernet adapter are not going to blink.
As long as there is nothing wrong with the cat.5 network cable and its connectors, then you have to enter your router's setup and make some changes here.
Most routers have a default URL and password to enter the router's setup utility and it is done through your web browser's address bar.