No access to set up modem or router

you might have configured your lan settings wrongly.

If your modem was setup for DHCP then you configure your lan to receive IP address automatically, DNS automatically.

If DHCP is disabled on the modem, you have to USE static IP Address for your lan ip and default gateway should be your modem default ip.

the default IP for modem is usually 192.168.1.1
if DHCP is disabled on the modem the sys ip is 192.168.1.3

So Configure your LAN setting as follow and Type http://192.168.1.1 in the address url.

Lan Settings:
IP Address: 192.168.1.3
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.1.1

click ok.
and type the above url, press enter the modem will ask you for username and password.

Good Luck.