blank screen on start , power but no chime

had this problem a while back , and got a pro to fix it , he said it was the cmos or pram in a mac .

all was fine till i left it on over night , it wouldn't wake up from sleep so shut down and the same problem came back .

tried reseting the pram by disconnecting the pram battery and unplugging machine for two hours .

still didn't work then i took out one of the ram chips and tried and again , this time i got a chime but still a blank screen .

so put both ram chip backs and went back to original problem