Dell Win XP Laptop acnnot take IP Address

I have a Dell Inspiron laptop with Windows XP, which was working fine with the Wireless Internet through the Trendnet Router. Recently I purchased a new Dell Laptop with Windows 7 and connected that to this Wireless Router as well. For the first few days, both the laptops worked fine, but a week back, the old one (Windows XP) did not connect to internet any more. The connection status shows “connected”, but cannot surf the net. I contacted Trendnet and after a check, they said there is no IP address in my laptop. When we tried ipconfig in the cmd prompt, nothing showed. Even when manually entered, the TCP/IP values were not getting changed.