First make sure the base unit has power (red light on base).
Then you need to place the 510 in pairing mode which is holding the Call Control / Answer End button down while pressing the volume up key till the indicator light on the headset starts flashing red then blue.
Press and hold both the talk volume fine tune buttons on the back of the base for a minimum of 5 seconds.
The blue button on the top of the base will come on and start flashing.
When the base light stops flashing and stays solid blue you should be paired.