What region are you located?
Are you wired or wireless connected to the router?
Has a Factory Reset been performed?
What ISP Service do you have? Cable or DSL?
What ISP Modem make and model do you have?
If this modem has a built in router, it's best to bridge the modem. Having 2 routers on the same line can cause connection problems.Double NAT
To tell if the modem is bridged or not, look at the routers web page, Status/Device Info/Wan Section, if there is a 192.168.0.# address in the WAN IP address field, then the modem is not bridged.
If the modem can't be bridged then see if the modem has a DMZ option and input the IP address the router gets from the modem and put that into the modems DMZ.
Check ISP MTU requirements, Cable is usually 1500, DSL is around 1492 down to 1472. Call the ISP and ask.
When you are connected to the 601, review the Status/Device Info/WAN section on the router web page, does it show the IP address or WAN IP and DNS addresses getting any thing?