Trouble Connecting to the Internet Through Router

My Windows XP Dell Inspirion connects wirelessly to my DI-524 router, and has done so effortlessly for over a year. But today, after the computer had been off for a few hours, I received an error when I opened my browser, saying "problem connecting, etc". I unplugged the router and modem for a period of time, and this did not remedy the issue.

I opened the "Wireless Connection," and was shown a message saying that I was using another program to manage my wireless. It said in order to manage my wireless with windows I needed to read article 871122. I'd never changed anything with Dell Wireless WLAN card utility, so I assumed that this was not part of the problem. Anyway, I googled 871122 and found out I needed to download Microsoft Fixit 50469. So I did, and now I can use Windows to manage my wireless.

But I still can't connect to the internet wirelessly. Although the wireless icon shows 100% connectivity, when I try to visit websites, I get 'problem connecting' errors. And when I type ipconfig in command prompt I get "not recognized as a command..."

I've tried connecting to the router with a cable, but I cannot get internet that way either. I've tried disabling my anti-virus and my firewall, doing a hard reset on the router, and unplugging everything for a few minutes, still, no luck. I can, however, connect to the internet if I connect the modem directly to my laptop.

The fact that I can connect to the internet while directly connected to the modem leads me to believe that the router is the problem. However, I don't think that router problems can explain how 'ipconfig' mysteriously became disabled or how I suddenly was unable to use Windows to configure my wireless connection.

Any advice would be greatly appreciated!