Internet not working through modem

I have a internet connection where I dont need a modem and the ethernet cable goes straight to the pc. Now my problem is that when I m trying to connect different computers through a router it works fine for someday after that it shows problems " Request time out " and "Destination host not responding" when I complained to the Internet Provider they say connection is fine from there end and there must some problem in the router. Then I removed the router and connected the ethernet to a single computer directly and it was really working fine. So I bought a new router and connected all the computers and it was working fine until the same problem appeared again. Till now I have changed 3 routers and the problem is still the same.
When I plug the ethernet cable directly the internet works fine but when I try connecting through router it works fine for some days then again the same problem.
Please help guys.
 
Does it fix the problem if you reboot all computers and the router / full power down, at least for a few days before happening again??
 
Connect the Modem Lan slot directly to the router lan slot, not the wan.
For this to work (and it does . . Using in as a type), the router must be configured to DISABLE DHCP
 
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