how is your networking set up? ISP modem to 601 then everything connected to it?
the IP address that comes from the 601 router defaults to 192.168.0.1.
Are you using the 601 router as the main router?
What HW version is your router?
What FW version is currently loaded?
What ISP Service do you have? Cable or DSL?
What ISP Modem do you have? Stand Alone or built in router?
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.
Turn off all anti virus and firewall programs on PC while testing.
Turn off all devices accept for one wired PC while testing.