Please excuse typos etc, i broke my wrist 2 weeks ago and am typing with my right hand using one finger!
I have an old desktop pc, windows XP and a laptop windows vista, which have been connected to my router and working together ok for 2-3 years. I noticed recently they share the same IP address. Out of the blue, 2 days ago, I found that my XP computer would not connect to the internet. After a few attempts I got a message from windows, saying the network did not assign a network address to the computer.They tried to repair it by getting a new IP address, then I got a message that it could not complete the action. I did not set it up myself, a friend did it for me, and the 2 pcs have worked together all this time with no problem. I cannot understand, if they are both connected though the same router, presumably using the same IP address, why is the laptop still working perfectly, and what can I do to get the other one connected when windows can't even do it?
What kind of router do you have, brand and model would be needed to help you figure out what to do with it.
You said both computers have the same IP address but that would be the external address being the one that the router actually has and is the same address that you would see on our home page.
For the computers to connect to the internet through the router they typically get internal IP addresses from the router by a method referred to as DHCP. The computer that is not connecting is probably not getting an address from the router.
On both computers, go to the command prompt (start > run > cmd > hit enter) type ipconfig and hit enter. Post the results. There is nothing there that is secret, sensitive or needs to be protected. They are all internal addresses and will be the same or similar to almost everyone elses information.
Also are the computers connected to the router by wired or wireless connections?