I'm travelling to hong kong nxt week,my destination is guangzhou how do i get to beijing by trains

hi,i'm travelling to hong kong nxt week,my destination is guangzhou how do i get to beijing by rails.i hear that the railways are scarce and the travel time is abnormal where in some instances people stand on feet over night due to the railway carriage being full.please can somebody help with this dilema and the costs involved,thank you in advance for your inputs.