OS X :: System Freezes And Display Goes Blank

I recently upgraded from my Macbook to a refurbished Macbook Pro and since the day I got it it has been giving me problems. Applications quite suddenly all the time and the system freezes and runs sluggish. The biggest prob is the display. It goes black and won't come back on. Sometimes when it goes blank you can see faintly if you look carefully and you can hear sounds. It slowly deteriorates from a once a week occurrence to a daily one until it won't turn on at all. I reinstall everything once a month. I took my computer to the mac store they ran all the diagnostic tests they have and said it is not a hardware problem. I have now wiped out all of my non-apple applications and the problem is back.