Few system settings you can check
In vista(classic view)/XP
Control Panel > System > Device Manager:-
Looking for "Network Adapters"
You should see something like "*Ethernet Network device*" (could be anything but it will be in the network adapters list)
and then just right click on the properties and check that its turned on and says its working.
- If its there and isn't working, try troubleshoot/update drivers and see if that works. (you may want to check that the network is enabled.)
- If its missing - its either broken or has been disabled on the bios (I dont have a dell handy to check the options @ the bios)
If it
is showing at the Laptop side, its probably your cable or router/modem.
If not, its either bios/hardware -- Hardware on Dell Laptops is fairly easy to work with and there are lots of guides about if you search for your model, but if you don't feel like risking it...
You can just go 108G wireless for around £35 if your on cable(virgin) or £55 for ADSL (BT/TalkTalk etc). (look for the bundles with a usb stick as they usually work out cheaper.)
If you already have a wireless hub, you could probably just get a usb stick for ~£5-10 on Amazon.