If a reboot doesn't help, it's time to consult the IT-guy. He might do something like reset the router. But he might not appreciate it if you do that yourself (assuming you've got access to it).
At work I use Win 7 Pro. I've used the same computer for many months with no problems or changes. It worked fine this morning. After lunch it would not connect to the internet or office network. A warning popped up saying that another computer was using my computer's IP Address. (!!?)
Why? What could happen to suddenly cause another computer to exist which uses my machine's address? How can I examine this and resolve it? If I get our "administrator" involved, he will make my whole desk inaccessible for a long time while he figures it out, so I'd really like to fix it myself if possible. I tried the ipconfig /release & /renew, with no success. I re-started several times, with no success.
Can anyone please tell me something else to try?