There could bemany reasons why you;re not seeing any playback.
what codec is your footage in?
What sort of drive are you playing it from? Not you system drive?
What are the settings of the project are you working in.
do you have lighting, depth of field, motion blur turned off?
have you set playback quality to low, note this is different from render settings, which will effect the render not the playback.
report back.
adam