Internet connectivity Problem

I have a Dell Precision M4300 laptop, win xp. It is
connected to the the internet via D-Link ADSL 502T router
Last night I lost internet connectivity, i have checked with my desktop PC there is working fine.
My next thought was a network card in the laptop. But, i have checked in Device Manager in Computer management, there all network adopters showing working Properly, even i'm able to access other computers through LAN that mean there is no Problem in network card
In Device manager i have 4 different network adopters
1) 1394 net Adapter
2) Bluetooth personal area network
3) Broadcom netxtreme 57xx gigabit controller
4) Dell wireless 1390 WLAN Mini-card

All are working properly

I tried to connect laptop by using USB cable from D-Link ADSL router, in this case internet connection is working properly ( in this case ADSL router act as a New network adopter). Then with out removing USB connectivity i connected ethernet cable (RJ45), strage!! now what ever webpages are opened using usb connectivity are working properly through ehternet cable connectivity even though i have removed USB network connectivity, but i can't open new sites either from IE or Mozilla Firefox.

So, the problem is I can't connect intenet using ethernet cable (RJ45 port), but i can connect net by USB port cable

Please, Can anyone solve this problem?


Thanks,
Chandru