over dub problem in logic x

ok , ive been using logic x for w while and done alot of recording , but for some reason all of a sudden when i come to do a overdub ( guitar for example ) i can only hear the guitar im over dubbing with when the punch in starts recording over previous track

i use to be able to have the track i wanted to record over running and also play along and hear both running into to the section i was about to record over

And also visa verse if i dont use the punch in option and just hit record to over dub onto a track i cant hear the previous recording but can hear the guitar im about to record over with

i know its probably a simply fix but its driving me mad

please help

thank you

tony