Default+Gateway+is+0.0.0.0+as+well+as+correct+address

So, for some unknown reason, your workstations that were working fine before now are getting a Gateway of 0.0.0.0 IN ADDITION to the proper Gateway, but the default is 0.0.0.0 so they can’t get online.
 * 1) Get to a DOS prompt as an Administrator
 * 2) Type route delete 0.0.0.0 and hit enter
 * 3) Type ipconfig /release and hit enter
 * 4) Type ipconfig /renew and hit enter