Switches problem

Hi!
I got a problem over here
My friend Owns A cyber cafe
He was using 100mbps ethernet
Not when he use hub everything goes smoothly
But when he uses Switch (INTEL) the network become Zero
We replaced the switch with another Switch(INTEL) butthe
problem is same,,,Now he is using Gigabit ethernet
So i wantto know that whatcould be the problem as we are not
able to troubleshoot that why is it happening
why Network Stop when we use Switch and is working when we use
Hub
Try to Provide all the reasons and the ways to overcome that problems
So that we can make use of those switches which are just garbage for us right now