You know that midi doesn't transfer audio? Midi really only issues commands. Also, you must have your computer Off and BR-1180 OFF, midi is not 'hot plug-able' like USB. Turn on the 1180 and than re-boot your computer.
First you need a 'Y' cord that has two male RCA on one end to patch the BR-1180's stereo line-out. The other end has a 1/8" stereo mini-plug, this goes to your computer's soundcard 'line-in'. The BR-1180 will only operate as a midi Master, so you to know what midi ch that cubasis needs to start recording. Once you press Play on the 1180 (and if the sync is right), cubasis should start recording.