What Hardware version is your router? Look at sticker under router.
version is currently loaded? Found on routers web page under status.
What region are you located?
Are you wired or wireless connected to the router?
What ISP Modem Mfr. and model # do you have?
I think all you need to use on the router is the following: Setup/Internet/Manual/Connection type: PPPoE and input acct and Password. Select Always ON. Save settings and reboot the router.
Power Off the 600L and ISP modem. Wired LAN cable should be connect on the internet port on the modem to the Yellow Internet port on the 600L. Power ON the Modem and wait 30 seconds, then power ON the 600L. Your PC should be wire LAN connected to the Black LAN ports on the 600L. The Internet globe or light on the 600L should eventually turn green.
Check Internet on the PC.