Ok, take a deep breath and relax.
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It's possible that if your on DSL, your DSL modem also has a built in router in which adding a another on on the line can cause problems.
First off, it's recommended to bridge or change the operating mode of the DSL modem to Transparent, effectively turning off it's router services. This makes the DSL modem, just a modem. AT&T can and should help you with this. Thats there responsibility.
2ndly, after the DSL modem is bridged, you'll need to enter in your DSLs PPPoE account information into the 601 router under Setup/Internet/Manual. This will tell the router to connect to the DSL modem and authenticate with AT&T as if the DSL modem would be doing it. Make sure the ALWAYS ON option is enabled if your 601 router has this.
After that, power cycle both DSL and 601 router. Let the DSL modem sync, the power on the router. Log back into the router and review the Status/Device Info. You should see under the WAN section ISP addressing information. I recommend copy and paste the Primary and 2ndary DNS addresses into Setup/Internet/Manual section if they aren't auto filled in.