Check to see your network card is properly inserted; it might have been knocked loose in transporting it back from uni.

If all the connections are fine, open up a DOS prompt and enter "ipconfig /all". If the IP address doesn't fit within the numbering scheme of the rest of the computers on the network (I'd expect it to be something akin to 192.168.x.xxx), then enter "ipconfig /release". Once that's done, do "ipconfig /renew". Provided everything is working fine, it should renew the DHCP in seconds, and everything will start working. Hopefully.

No guarantees any of this will work, but I've had a fair amount of fun with networks over the years XD