DIAGNOSIS The speaker is either already connected to a remembered device, or it's stuck in a non-responsive state.
FIX Power the speaker on. If the Bluetooth LED is solid (not blinking), it's connected. Press the Bluetooth button once to disconnect and force it into pairing mode—the LED should start flashing.
IF THAT DIDN'T WORK Clear all paired devices: with the speaker on, press and hold the Bluetooth button for 5+ seconds until you hear a sound and all LEDs flash. Then try pairing anew.
HEADS UP The Charge 5 can remember only one device's connection at a time for phone calls, but up to two for audio playback. This can cause confusion if you're switching between multiple phones.