(1) Make sure in the settings on your phone that it is not set to silent. If its on silent turn the sound on. (2) Look into the headphone jack and make sure there is no debris in it as well as where your speaker in the phone is. You may want to blow air in them just to make sure. (3) Your phone maybe linked to a bluetooth device. Check to make sure bluetooth is turned off. (4) Try turning phone off then on again restarting the system.
(1) There may be something stuck under the key. Make sure nothing is in the way under your keypad. If so clear and then clean the debris, and check for water contamination. (2) If that is not the case look for wear and tear. Remove your keypad (all one piece, can not check individual keys) and check to make sure all the keypad sensors are working correctly. If they are not you may replace the broken sensors. This can be found on the replacement guide.
(1) It could be the charger itself. Make sure there are no frayed wires, bent or damaged connection pieces, or the resistor inside the charger. (2) Next make sure there is no debris inside the charging port, in the phone itself. (3) It also could be the battery. You may have an old or damaged battery which you may need to replace, in which case see the replacement guide for this device.