WHY IS THE GREEEN POWER BUTTON FLASHING ON MY MONITER AND THE SCREEN THEN GOWS BLACK

When the power light is flashing the monitor is not getting a stable signal. This is hard to answer without direct troubleshooting. Check the cables first, make sure they are connected securely. If you still have problems test another monitor you know works or move monitor to a computer you know works, this will determine if the monitor is the problem or not and tell you if it is your "graphics port or adapter". If another monitor works fine, use the working cables to test the "broken" monitor. If you have an "all-in-one" computer, ignore the above steps and use a start-up repair disk. The reason this is hard to troubleshoot is there are so many things to diagnose. More than likely your "graphics card" is failing. These are some tricks to repair. You can update the driver, buy a graphic card separate from the stock port.