Sharing broadband router with linksys BESFR41 V4.0

[Maximus()]

I have a Linksys router BESFR41 V4.0 four pc are connected and the local network is functioning normally but it is impossible to simultaneously access internet effecting one with internet other pc . I want to say that I am not an expert in computer science is an explanation why not me too complicated facilitate.

advance thank you.

[ArtisticVisions]

Have you checked the DHCP on the router, and do all the computers automatically obtain an IP?
What are the IPs obtained by computers? (Start, Run, type cmd, then type ipconfig / all) computers have the same bridge?

The modem (ADSL or cable) is plugged into the WAN port? :p

I know it matters beasts, but all know all the facts

[Maximus()]

dhcp enabled on the router with speedtouch 510v.5 modem connected.