Hello! I’ve recently connected my key board to the computer, and everything works fine, exept for the fact that when I try to put one record “on top” of the other (excuse me for my bad english) like making pitches or whatever you call it. Yesterday I tried, but when I started the second record I could only hear what I was playing for the moment. When I later pressed “Play” I heard both. But I really need help, it’s very hard to comp without hearing the instrument you are comping. Please, help me… 
In 1.2.x go to Edit > Preferences > Audio I/O and check the box that says “Play other tracks while recording new one”.
Or if you are using 1.3 (you don’t say) Edit > Preferences > Recording and check “Software Playthrough …”
WC
Thank you very much, that solved my problem 