Plugged in a different PC to ethernet and now my router is a complete dud.

Ok so I have a unique situation. I plugged in an old pos (piece of shit) computer I got for free yesterday just to see if it worked. I unplugged the ethernet to my usual PC and and hooked it up to the pos one. It turned on, it ran windows xp but wouldn't connect to the internet. When I was through, I plugged in my rig and I had no internet. Now my situation is unique because I live in a back house and we all share Internet. The main modem for everyone is in a case in the middle of the property, I do not have access to it as its behind a gate and in my neighbors yard. My router for my unit is next to my computer. My router usually plugs into the wall and gets Internet through there, then my pc plugs into the router. Well, every since I plugged in the old PC I get the error code 651: the modem or other connecting device has reported and error. I've tried with no avail to enter my ip address into Google to get the router setup but I'm just greeted with a page saying "management mode firmware upgrade" and it prompts me to choose a file to upgrade the firmware. I have since downloaded those at work on a USB flash drive but I can't get that managemrnt screen anymore. It just says Web page not available. Before, I would enter the ip 192.161.1.1, the default linksys router ip I believe. Now I don't get jack. My pc will not get Internet even if I plug it directly into the wall, but my wife's laptop has internet if we go through the wall. I'm really at a loss of what to do next. I can't ask my neighbors for help because I don't know them that we'll and they probably wouldn't know anyways. Since internet is shared I don't have an account with at&t so I can't call them and linksys was absolutely no help and stated since my router was outside the warranty I would have to pay $20 for support. I don't have $20 right now I'm pretty broke.... if I could just access my router settings I think I could figure it out. I've reset them be router and unplugged it and all that. The router is a linksys E2500. Any help would be greatly appreciated. Sorry in advance for typos, I'm on my phone. I'll try to post some images when I get a chance.