What is the exact model number and version number of the router by the way? If it is a v5 or a v6, then update the routers firmware first. To upgrade it automatically, go to www.linksys.com/easy and run the EasyLink Firmware tool. This one should assist you in upgrading the routers software. Make sure all firewalls are off though.
After you have done that...Do this exact process:
► modem goes into the internet port
► main PC goes into port 1 (or any of the numbered ports)
To configure the router
► open up IE and type in 192.168.1.1 on the address
(username just leave it blank / password is admin)
► go the MAC Address Clone tab
- enable and click on the clone button
- save the settings
► then turn off in the ff order:
► reboot in the opposite order
This process should hopefully at least get you online wired to the router.