Are you using static IP addresses? If so, check the computer NIC IP address settings on all computers. If using DHCP, open a command window on the problem computer and type
<b>ipconfig /release <enter></b>
<b>ipconfig /renew <enter></b>
This should assign a new address to the computer unless there is a reservation in DHCP. If there is a reservation, then you need to go to the other workstations in the network and see if one of them has the problem IP address assigned. Perform the /release & /renew tasks on that computer after changing the settings to DHCP.
Let us know how you get on.