Suddenly , my device no longer picks up the signal from the chest strap. My Garmin GPS picks up the signal and displays my HR right away. I have "removed" all sensors from the device and tried pairing again several times to no avail. Also, when wearing the device with no chest strap the reported HR is way off and remains stuck at a single number even with widely varying exercise intensities. The device is 6 months old and the battery is charged. Any ideas for trouble shooting?