Most cables simply plug in to the base of the handset. You should check that the cable is securely connected at both the phone end and at the PC end, and that it is configured as per the manufacturer's instructions.
Some cables require the rear cover of the phone to be removed, and some also require the battery to be removed. Ensure that all the contacts on the cable are making a good connection with the exposed connections in the phone. Also, if you removed the battery, ensure that it is replaced and that the phone is powered up while the cable connected.