Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble.
You may have the system in intercom mode, OR a hardware failure in the base station (since the issue happens with all handsets). We most often see this type of damage to the base unit as the result of a power surge, either through the phone or power lines.
Initially try pressing the speakerphone (SP) button on the main base, twice, and see if that helps. If not it points to a hardware fault and the one thing you may attempt yourself is to fully reset the system:
1) unplug both power and phone lines from the main base.
2) remove batteries from all handsets
3) wait at least 15 minutes, then restore all
4) place a handset on the main base for a minute, as if to charge
5) check for functionality.
Let me know the results, and I'll advise further if needed.