After turning power on screen turns off after a few seconds

Mike this means that one or more capacitors in your monitor is faulty. A bulged or leaking capacitor would cause that. Capacitors hold power from the source long enough for your display on the monitor and if the capacitor is faulty it might not hold the power long enough for display. As a result of this, the monitor is able to give display only for about 6 to 8 seconds and it switches off.
To solve this problem, you need to open up the monitor, using a long and sharp tool to perfectly separate the two covers. Make sure that you take note of the finger-like structures that are holding the two covers together, do not break any of them, they are the only supporting structures, holing up your monitor in cover. Make sure to open the monitor from the bottom, working your way round to the top. When you succeed, check the power circuit board of the monitor( Where the power cable is plugged), and check for any leaking and bulged capacitors. When you do, make sure that you take note of the ratings and the colour codes on the capacitor, and be cautious of the position of which the capacitor is placed on the circuit board so that when you replace with a new one, it is replaced exactly as the old one was placed., This is done to avoid negative with negative or positive with positive......
I hope this will help to solve your problem Mike