Make sure that when you removed your screen you didn't accidentally unplug your NIC or wireless module. The connectors are very small but when plugged, they shouldn't become unplugged. some manufacturer's put the wireless antenna along the screen edge, so you could have accidentally removed it. Failing that, try reloading from your original drivers disk. Failing that, find a reputable laptop repair shop. Failing that, find a dust bin and buy a new laptop.