Lose network connection

Probably at least once or twice a day I lose all network connectivity at my workstation. I am on a network with 300 other people, all of whom have no problems. The connection usually fixes itself after about 5 or 10 minutes. I have replaced the NIC card multiple times, I tried plugging into a hub with a neighbor, I took myself out of the domain and re-added myself again and again. Does anyone have any ideas why, without warning, I lose connectivity.