Do you have any DVDs that came with the computer? They may have driver copies on them.
If not open Device Manager and go to Network Adaptors.
Find the name of the network adaptor device.
On another computer, search for the device name and drivers, probably on the Dell site. Download the driver installation software and put it on a USB stick, transfer it to your laptop.
Did you just uninstall the LAN driver or the wireless card driver or both? If the first, try using a wireless connection to go and get the replacement driver, if the second, try connecting the computer to your router with a network cable. If the third you will need to use another computer unless you have the driver disk somewhere.