You can try re-installing the LAN driver again and see what happens! or this may be a problem with your cable!
Maybe a bad LAN chip in your laptop if reformatting did not work. If you are using the LAN driver provided by Microsoft, uninstall it and try using a different one. Download one on another PC, and copy it to the laptop with a USB memory stick or something. Could be a bad BIOS setting. Does your laptop have wireless? Maybe the LAN and the wireless are conflicting with each other. If present, disable the wireless receiver in Windows on your laptop then try plugging back in your DSL modem.