Network problems

G’day y’all. I have a network of 16 desktops, all running xp pro. I went to work this morning and found that i couldn’t connect to the internet. I use a dsl modem and a network switch to provide net access to all computers. the modem indicates that everything is connected, but i still cannot access the net. Everything was fine when i last left it on wednesday. I notice that the ethernet light on the dsl modem comes on and off periodically. could this mean that my network switch is failing? If that’s not it, i would greatly appreciate suggestions as to what might be happening.
Thanks much, and God bless y’all