Cubase AI6 and Yamaha N12

I’m new to this forum and indeed Cubase so if I am not following the correct etiquet please forgive me - I have tried to search for an answer to my problem.
Basically I seem to have set everything up in accordance with the manuals, but when I play back the sample recorded track the audio breaks up in places and cuts out. I have tried various suggestions that I have found but the problem persists.
I can confirm that it is not audio clipping.
I’m running Cubase on a Dell Precision M6600 on Windows 7 Professional 64 bit with 12 Gb RAM.
If any one can assist me with this I will be very appreciative, If more information is required I will happily provide it.