try to power cycle the cellphone by turning it off and remove battery, then reinstall and turn it back on
For headset pairing
How to pair the phone with a Bluetooth™ headset
The phone identifies and maintains up to 16 devices which are displayed
in a list. To add a new device or pair a headset via bluetooth, turn
Bluetooth™ on in both devices.
- Put headset in pairing mode. See Headset User Guide for more information, if needed.
- Turn on Bluetooth in your phone, Go to menu, [SETTINGS] > [CONNECTIVITY] > [BLUETOOTH] and press "Select"
- Choose [TURN ON] , press "Select"
- Choose [MY DEVICES], press "Select"
- Choose [NEW DEVICE], press "Select"
- Choose the headset to be paired and press ' Select '
- Enter the pass key '0000', press "Ok"
Link for headset setting, just choose the headset model
http://www.sonyericsson.com/cws/support/products/pairinginstructions/w300i?cc=us&lc=en
If you are using a different device the just set the Bluetooth to on on it as well