networking problem

i have a very small company with only a 5 computer network, so i run it off a windows xp machine. it connected through a wireless network router, and has been for the past year without any problems. suddenly, the server stopped being able to access the internet, while the other computers can. when i check the ‘ipconfig/
it doesnt come up with a default gateway. also the computer says that a cable is disconnected..it isnt!!
what im still shocked at is the fact that the other computers are able to access the internet
:s
please help