Check your MIDI cable(s) for bent prongs or any other problems with the connector or wire. MIDI connectors have five prongs inside a metal connector ring approximately 1-inch long. If one of the prongs is bent or missing, the MIDI cable will not transmit MIDI data correctly.
Make sure the MIDI cable's connector is seated properly when inserting it into any MIDI jack. The connector must be pushed all the way in for a complete connection. The plastic at the base of the metal connector should be flush with the rim of the MIDI port.
Connect a MIDI cable to the "MIDI OUT" port on a MIDI control device, such as a MIDI keyboard. The "MIDI OUT" port transmits MIDI data to other devices. Connect the other end of the MIDI cable to the "MIDI IN" port on a second device, such as a hardware synthesizer. The synthesizer will play the notes triggered on the MIDI controller. In rare cases, a second MIDI cable must be connected between the MIDI controller's "MIDI IN" port and the hardware synthesizer's "MIDI OUT" port in order for the devices to interface properly.
Connect a MIDI cable to a device's "MIDI THRU" port to send all MIDI data received by that device's "MIDI IN" port onto other devices unchanged. For example, using the scenario described in step three, a MIDI cable could be connected from the hardware synthesizer's "MIDI THRU" port to the "MIDI IN" port of a second hardware synthesizer. Both hardware synthesizers will receive and play back the MIDI data from the MIDI keyboard. This set up is called "daisychaining."