1. If it rings only once and goes to silence on the calling party end, there is a high resistance short on the line and it must be repaired.
2. Double check whether the ringer is on or not.
3. Check the weather when experiencing this problem. Electrical storms, heavy precipitation, excessively strong winds and other natural phenomenon can interfere with phone reception -- particularly if you're using a cordless phone. If this problem only happens when the weather is bad, try again when the storm has passed and/or switch to a corded phone.