Had a problem with my Dell laptop similar to yours. I hadn't used my Dell laptop for a few months and recently when I tried to connect to my D-Link router (connected to cable modem) I could not get the internet. Firefox and IE would start OK but would give the "page not load" (or whatever) error. I have a second PC/desktop connected to the same router via LAN and it works fine.
- I tried both the LAN and wireless connections without success.
- I checked both the LAN network and wireless adapters in Device Manager and both were fine but even so I downloaded and installed the latest drivers from Dell.
- Released and renewed the LAN connection several times.
- Uninstalled my firewall but that didn't work.
- Installed Cisco's Network Magic and it couldn't find the problem.
- Reset the Winsock with no difference.
- I had a copy of Vista purchased with the laptop and installed that and that too wouldn't give an internet connection.
- Checked cables; rebooted (power off/power on) the router and the modem.
- Finally I tried the laptop at a friend's place that had a similar router/modem setup AND IT WORKED!
So I went back to mine and looked over the router and found a "factory reset" button and did the reset and viola it worked! I think there is a software way to do that too.