NETWORK HELP!!!! FAST!!! PLEASE!

hi i have 2 computers, they had a perfect network going. File sharing and all, then after awhile(dunno when exactly) 1 of the computers does this– I plug the ethernet wire in, it shows the connecting symbol on bottom left. Then says ” Aquiring network address” for a min then says “limited or no connectivity” with no packets recieved. Just a couple sent. EH! what do i do? i tried installing the network driver again. same thing again. help me please!