fiasco

hi any help or ideas on this matter would be greatly appreciated, my pc recently would not start when i hit the power button nothing happened, i replaced the psu with a new supply and the computer powered up fine however even though there was power to the monitor nothing came on screen and the green light just flashed on and off on the front of the monitor. i replaced the graphics card with a new one and still the same problem no apparent communication between pc and monitor, i would like to know whats wrong or how to fix this before i go buying any more new parts so i know how to fix it for sure, thanks for any help and advice, fiasco