Can anyone tell me why I can`t acess to the internet qhen I install the DD-WRT firmware?
I identified several problems from your screenshot.
First of all your LAN settings on the modem use 192.168.1.1 and have DHCP enabled, but your DD-WRT uses Static IP. Maybe you want the router to always have the same IP on the modem - router LAN, not like it would matter, but fine. Then why keep DHCP server enabled? Anyway, this is not such a big deal.
Now, from what I can see your DD-WRT WAN settings have no DNS server specified. This means domains won't resolve. Either set your DD-WRT WAN Connection type to "automatic configuration - DHCP" so it can get the DNS from the modem automatically, or set a DNS server manually under Setup > Basic Setup > Network Setup > Local DNS.
This gets us to the next problem on the DD-WRT router. Your LAN subnet conflicts with the WAN one. I see your home computers are also 192.168.1.*, that's not how it works.
It must be a different subnet. So, once you have 192.168.1.* between your modem and router, where your modem is 192.168.1.1 and your router is 192.168.1.2, but it can be whatever on that subnet.
Your LAN settings for router should be a different subnet, like 192.168.2.1 or different entirely 10.0.1.1 for router. This is set from Setup > Basic Setup > Network Setup > Local IP Address.
If you don't understand something from my hasty explanation, feel free to ask.